Thanks for the replies guys.
@ Vernon, I don't think it's my hard-drive, I recently did a reformat and I basically have nothing on it yet apart form a few games. I CClean regularly too..
I don't know what brand my PSU is. I'll check it in a sec and post it.
Edit:
My PSU is only 350watts... I thought it was 450, Lol. It's made by a company called 'Atlas'.