XP and Vista are out of question, 7 and 8 only.

If you have registration for any of those other windows you could enter that during installation if it would not activate otherwise. Actually you can do that even in already installed but not...

If W10 was ever activated on that computer all you have to do is to install it clean using an appropriate ISO from MS. Mount it as bootable on a USB and start new installation keeping nothing. During...