Crashing while playing WoW

[Hadenn]

Alright heres my problem lately ive been playing WoW and my computer crashes up and everything just freezes up. I just finished puting in 512 of more RAM in and i thought that maybe this was the problem so i took it out and i tryed to play nd still it crashes. Before all this i started to hear like a huming sound from my PC that would get to a high pitch so i thought it might be the fans are not working properly and im overheating. I opened my PC up plugged it in and turned it on and the noise went away so i dont know if it might be the fans that are not working or maybe the hard drive is failing on me. So please can somebody tell me whats going wrong if its fan not working well anymore or hard drive or anything else.