OrbitalTrooper :
I built a PC back when windows 8 released and that computer had had HDD failures and now the whole thing is just toast. I'm going to build a new PC but I don't have the budget of being able to re-buy windows 8 so can I just use the old Win 8 install disc and activation key or will I need one of those programs that illegally activates it for you?
Please note a few keywords to make sure we are ALL discussing the same thing. As SR-71 linked to, if you used a System Builder edition of Windows, then you can move it from one PC to another, BUT you will have to do some telephone dancing with Microsoft to get them to manually activate it with you (type in the numbers to activate by phone / have a person assist). Secondly with Windows 8.1 you can NOT backup your data via Windows Easy Transfer, this has been permanently disabled. All data should be in the folders that sync with Windows LIVE! This will cause you on your new computer, to login to your LIVE! account and pull down all your data it has stored on the Microsoft servers.
IF your talking you had a PC that WAS built by a OEM (HP, Dell, etc.) and you may have swapped ALMOST all the parts out yourself EXCEPT CPU and Mobo, then that OEM is still LICENSED to the same old terms it can't move to any new hardware, and is ONLY tied to that hardware it was sold with.
As for the last part " or will I need one of those programs that illegally activates it for you"; Tom's Hardware does NOT support nor allow discussions about illegal activities like PIRATING SOFTWARE. The mods are very quick to not only delete posts, but ban whole accounts of those violating the outlined rules you agreed to when you joined the forums.