Can I reformat the HDD on a store-bought PC and reinstall Windows 10 from an NTLite ISO?

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I had no experience with Windows 10 until several months ago when a neighbor gave me what she thought was a broken HP All-In-One. She didn't want it back and said I could do whatever I wanted with it. I did a factory restore to whatever version of Win10 was current 5+ years ago and have since updated it to be current as of October 2025, and have made several Win10 images with NTlite with the intent to reinstall. This is the first store-bought PC I've ever had. I've built all my others from parts.

I actually have reinstalled several times, but from within Windows. I click on the setup.exe from within an NTLite source and sit back and wait. When it's done I have a new Win10 install, but also a Windows.old folder that I then delete. I'm used to starting with a fresh HDD, so this seems like a "dirty" way to install Windows. Ideally I'd like to reformat and start fresh. It has a 1 TB HDD with almost all of it dedicated to C:. I defragged, went into Disk Management and shrunk C:, and used the extras space as a storage partition where I've been keeping the NTLite sources.

Here's my issue - I have a terrible understanding of how activation works. With the way I've been reinstalling so far everything has gone fine and Windows has reactivated automatically.... but how? I assume it's because a new install sees the activation key/license that's already on the PC from the previous installation. I've been too paranoid to try reformatting and reinstalling because I figured I'd lose activation (at least automatically) because I'd be installing to a blank HDD, so there wouldn't be a pre-existing installation with a key to see. I know I can pull the key from the registry using a utility, but can I successfully use it if I reinstall to a blank HDD with an NTLite source? I didn't want to try it without asking first.

I like the idea of doing a clean install, but even if I can... should I? Or should I just keep re-installing from within Windows until I get the NTLite mods I'm happy with? I know I'm not going to get a 25% performance gain just because I started from scratch vs. reinstalling from within Windows, but I'm not used to doing it this way and for whatever reason it just doesn't seem like the best way to do it.

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There are several legitimate methods for activating a Windows system:

1. Provide a specific activation key (not generic install key) in the unattended file or the ISO's PID.txt.

2. Your PC has an OEM product key in the BIOS (normal for brands like HP or Dell).

3. Your PC was previously activated, and MS created a online digital activation where it remembers this PC's HW ID. As long as the system HW is unchanged (which is always the case for an AIO model), then you don't need to do anything.

Digital activation will preserve the Windows edition even if it's different from the OEM product key. For example, the PC shipped with a Home product key but you activated Pro instead. MS will remember it's Pro moving forward when Windows tries to self-activate online.
 
Thank you. What would you do if you had this PC?

I'd only recover a little over 18 GB if reclaim the current E: drive and the unmarked recovery partition.

BTW, can you suggest a utility that'll let me do something with those 2 partitions? There's nothing but 'help' in the context menu when I try to access them in Disk Management.
 
HP and Dell will create specific Recovery partitions for themselves, so users can do a Factory Reset and get all the default vendor apps. If you know where to find all the required drivers, then you don't need to preserve the factory Recovery image. Any other vendor software, like tools, can normally be downloaded from their support website.

I would do a clean wipe and install. It's faster than trying to resize partitions and move things around. Personally I don't like splitting a single disk into C: & D: volumes. That's because you guess wrong on the partition sizes. Sometimes you need to grow Windows, and sometimes you assigned too much space to it (so it's wasted for user data).

Without the HP factory partition, you should follow the current MS guidelines:
- EFI is 260 MB​
- single partition for Windows + user files​
- Recovery is 980 MB​
 
" Can I reformat the HDD on a store-bought PC and reinstall Windows 10 from an NTLite ISO? "
You can do whatever you want with it! You can even plant flowers there—it's up to you what you do with it!
You can install whatever you want.
What would I do first?
- Add 8 GB of RAM
- Use the hard drive you have for data, backups, etc.
- Buy an SSD and install Windows on it the way you like.
 
I don't know if there's room for a 2nd HDD inside, even if it's an SSD. I'd have to take it apart and look.
 
If you don't have space for a second drive, buy a Disk Enclosure SSD HDD SATA 2.5 USB 3.0 and put a new SSD inside.
Don't worry about activation because it's the least of your problems - it's not a problem at all.
 
There are "tear apart" videos for many OEM machines and Dell has their own disassembly instructions. I don't know about others like HP. But search the web for "brand model tear apart" and you should find some videos. They usually cover things like RAM, SSDs, etc.

And yeah, I've been using my NTLite custom ISOs on my own DIY PCs as well as on Dells and my ISOs are based on the vanilla ISO available from Microsoft, not the Dell OEM ISO.

The only caveat is, of course, that the Windows editions must match. So, if your Dell, Acer or HP came originally with Home edition and your NTLite ISO is Pro edition then it won't activate. However, Windows can be used without activation just fine. There are many blogs and YT videos that talk about this. It will be fully functional with only few annoyances that have workaround to some degree.
 
Thanks. I'll be using the same edition so no worries there. I have PDFs of the documentation that came with the PC so I'm not worried about taking it apart

After doing some more reading I've come to realize that Windows 10 automatically installs those extra partitions. I thought they were put there by HP. I was too preoccupied with other things and wasn't putting 2 & 2 together. Win 10 has built in factory restore/recovery options.... and that's where all those files are. Seems obvious now.

My current thought process is to leave everything as is and reinstall from the command prompt using Diskpart, with the source files on the storage partition I created.
 
Windows creates 3 or 4 partitions (I never paid attention to how many there are actually) but OEMs can add their own too, for their own recovery tools. If your intentions are to do a clean install of a custom build then removing those partitions and starting with a blank drive is better, it'll result in a cleaner system without any cruft and artifacts. Otherwise, your new install will inherit a lot of problems from the previous install and your mods may not even work well or at all. You may end up with a weird and unstable Frankenstein build.

Clean install always yields better results, but yes, it is more time consuming and requires more effort and preparations, but in the end it's almost always worth it. The older the system, the more likely you'll end up with issues when doing in-place reinstall. In-place reinstall may seem like a time-saving approach but it often isn't.

Just make sure you have proper backups of your files (actual files and also AppData settings in at least in two separate places), as well as your software installers and drivers. Once those partitions are removed all files on them are gone.

Download everything you may need prior to installation, unzip and copy to an external drive. I copy my installers, drivers and some settings to the same USB SSD I have my Windows ISO burnt to, saves time.
 
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After doing more reading I came across info about applying an image using DISM, so I rebooted the functional Win10 system into recovery mode and reinstalled from the command prompt. I used DISKPART to format the C: drive, and installed from the source files on D:. I've done this several times over the past few days. Applying the image only takes 5-1/2 minutes, so it's much faster.

By MS standards this wasn't a 'clean' install since I only reformatted 1 partition and left the others alone, but wouldn't files on the System and Recovery partitions that get created during a 100% clean install be identical to what's there now? I wanted a clean C: drive, and that's what I'm getting. There's no Windows.old folder anymore. My files on the D: drive are left untouched so I don't have to back them up before each install.

I don't consider myself 'educated' about any of this stuff; I'm just a more advanced home user who can read and follow directions, and as far as I can tell, this method of using DISM to apply an image is working perfectly.
 
Actually, the way you did this was quite advanced :D (where is the thumbs up emoticon?) I never attempted that myself. I just prefer to boot from a USB, nuke the partitions and clean install. But, yeah, since you wiped the C drive then it's pretty much a clean install as far as I can tell, since that's where the cruft usually remains: old dlls, old drivers, old settings, etc. The other partitions are probably overwritten by the process.

It looks like you should be good then :)
 
Oh, this is why I use USB SSDs, not flash drives. They're significantly faster, 10-20x or better, than even the fastest flash drives. It takes about 15-20 seconds to burn an ISO to one of these and installations are very fast too. I never timed it but the installation from a USB SSD only takes like 2-3 minutes. My ISOs are 100% unattended and I got this down to science so I never considered making any changes to my process.

It seems, the only advantage of using this DISM method is speed, thanks to the image being on another internal SSD. So, I doubt I'd benefit much from this compared to using SSDs as my installation media. I build my own. Even a very old NVME SSD in a decent USB 3.0 enclousre can R/W 400-500 MB/s. I actually use USB-C 3.1 or 3.2 with newer PCs (if they can boot from USB-C), which gives me 1000 MB/s or more R/W.

So, I doubt I'd benefit much from this but it's definitely a valid option otherwise.
 
Wow, that's crazy fast. I haven't explored 'modern' hardware like (USB SSDs) in years so I don't even know what's out there. Thanks for mentioning what you use or I'd continue to be in the dark. I was thinking about cloning the mechanical HDD in this PC to an SSD, or maybe even an M.2 version as the documentation that came with this PC says it supports it. I'll take it apart and look at some point.
 
I started doing this way back in Windows 7 and maybe even XP days. Even a mechanical hard drive on a USB 2.0 bus was much quicker than a CD, DVD or flash drive. Even the most expensive USB 3.0 flash drives these days only write at about 10-20 MB/s, they may read 100 MB/s, but that is still far cry even from a SATA SSD which can R/W over 300 MB/s.

You can buy USB SSDs in a physical format that looks like a large thumbdrive, a bit bigger, they don't always fit in tight spaces, I prefer USB SSDs with a USB cable. Also, DIY gives you the best performance as those pre-built USB SSDs usually use cheaper and slower memory. But they still R/W around 150 MB/s or more.

You can re-use any old SSD for this and enclosures are fairly cheap, usually below $20. It was a game changer for me, it makes testing and installation so much faster that I don't remember the last time I used a flash drive for anything.

My preferred setup is an NVME M.2 SSD in a USB-C enclosure, they're backwards compatible down to USB 2.0 and they work with USB-A ports too but they all support UASP and TRIM and many SATA enclosures don't.
 
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