The C: drive on our oldest PC (8 years old, running Windows XP) is starting to make some ugly noises. I'm afraid it's about to crash. We don't use that PC for much other than web browsing anymore, and I've already backed up all my important documents. Now I'm wondering: if it crashes and I buy a new C: drive for that system, will it let me re-use its Windows XP license key? Or will Microsoft say, "sorry, that license key has already been used, please buy Windows again". While the current C: drive is still alive, is there some sort of "license file" that I can back up to cover myself?