Resetting Windows 7 / 10 PC?

I've posted here before, about the problems and challenges that I was experiencing with my older PC, after upgrading from Windows 7 to 10 last July. I finally just made the jump to a newer refurbed PC with Windows 8.1.

I have ( as far as I know ) everything transferred over. I reinstalled programs and moved data. Then finally, I cloned the old hard drive twice and put those clones in the safe.

So now, what to do with the older PC and it's HD. I'd LIKE to reinstall Windows 7 on it again, and sell it to someone who can use a Windows 7 PC. But being IT was a refurb when I bought it, around 2009, it didn't come with an OS disk.

So it's been upgraded to Windows 10 now, but that doesn't play well with the old hardware and is not worth messing with.

IS there a way that I can revert the OS to Windows 7 without having a disk, now that it's shown as being upgraded to 10?

I mean, I'd think that Microsoft has some kind of record that it was originally legitimately a Windows 7 PC, and I could reinstall it somehow?

You would need a product key to activate the Windows 7 on it. Is there a COA sticker on the computer with a Windows 7 product key? You could also, possibly, pull the old Windows 7 key off the backup of the old hard drive that was upgraded to Windows 10 using Showkey Plus from this forum.

AddRAM said:

If you have your W7 key.....

You don`t uninstall anything, you just delete the drive to unallocated space and install Windows 7.

Clean Install Windows 7 - Windows 7 Help Forums

I don't have a disk. This is a refurbed Asus that came with Windows 7.

AddRAM said:

Well then, download W7 from here.

Microsoft Windows and Office ISO Download Tool

Just run the Windows ISO Downloader.exe, you can then choose which OS Iso file you want to download.

Mine says: Windows 7 HomePremium OEM:COA
but that's not listed among the download options.

Ah ok, thanks! 3GB downloading now... Then I'll put it on DVD.

That's an interesting sig graphic that you have there, because my newer refurbed PC is an ASUS M32BC and I'd like to add to the 8GB RAM if it would significantly improve performance, but there's a seal on the case saying it would void the warranty. I got it in October.

Would also be awesome if I could figure how to do a SSD for it.