If it's windows 10 you probably need to reactivate your copy as it's tied to your motherboard. Maybe windows 8.1 does it too.
However, if I were you, I'd clean install. It makes everything neater. And now is a pretty good occasion.
But, if you don't: Windows will pretty much run on any new hardware.
I once installed an SSD that used to be a Wintel boot-drive in a macbook, booted up the mac to format and install OS X, didn't get the button combo right at "post" and it startede windows. Initialized drivers for a minute or too and bam, Windows 8 was running like a dream. Very impressive.