Here's what you can do.Install a windows 7 into your hdd from another computer.Then come put it back and switch on your pc.let it load and if it opens then switches of it will be ynur fan/hitsink with the problem.if it restarts whle loading,its still fine,it will show u two options choose the repair sytem option.repair the system.let it reboot.it should now be fine if not consider changing your ram and fan.if it doesnt work you wil only have one option left get a new cpu.it might have been damaged from overheating