Well, when you are OCing, you know that you are taking a chance to make things run above their rated speed and anything can happen. Your RAM may be working for a while and suddenly it goes bad so I don't think it has anything to do with Windows 8.
If you look at my system specs, you'll see that I also OC'ed my PC and I have no problem whatsoever running Windows 8.
Of course you'll need a good cooling when you are OCing.