Ok I posted back a couple months ago about the same problem basically. You can view that here http://www.techsupportforum.com/showthread.php?t=52960 I have yet to change the heatsink. As said before I keep my pc running 24/7 and about 3 weeks ago my pc just shutdown/rebooted itself. No weird fan noises this time, no freezing, just shutdown and rebooted back up. After that I decided I'll buy a heatsink(thinking most def this is the prob) in the next couple of days but I still want my pc running so I put a normal sized fan(took out my case covering) and let it blow into the pc. 2 weeks everything was going good until today when the problem of shutting down happened again. After it booted back up 15 minutes into working it happened once again. I was told it could be the power supply(350 watts) and that heatsinks doesn't really go bad and maybe I should try installing more fans. I was also told this is normal because I keep my pc running for long periods of time. I'm pretty sure my memory is fine and is intact. These are my details right now with the normal size fan blowing according to EverestBefore I put the fan in my CPU was around 150 *F. I'm not sure exactly the temp but it was hot. What could be the real problem? If you need more specs tell me. Thanks.