Always a clean install with me....I have 2 different USB's..one is UEFI/GPT..and the other is MBR..Same results...Yes I have it set to boot from the USB and appears it is doing so but then goes back to the Windows 7 logon screen.
You can install W10 on another machine and then activate it on another. I can't see where the problem is supposed to be. Anyway back to OP's problem there are Just some notebooks that are incompatible with W10. No matter if the meed the system requirements or not. I faced myself a couple of Asus that works perfectly with w7 and w8, but becomes useless bricks with w8.1 and w10 Just live with that. Possibly the BIOS is the culprit, and if like in my case there isn't any update done W10 can't be installed. Period.