This is a long story, I'm sorry, but it all helps the solution, (i hope)
About a year ago, my computer would get hot and shut itself off after about a half hour of use, as a safety feature. I replaced the northbridge fan with a large heatsink, hoping this was the problem. it wasnt. So about 3 months ago, my wife got a new laptop, so i was going to take over her old computer, but there were somethings on this computer that i wanted off. So i turn it on, get aas much stuff off as possible and then it shuts off. it does this about 3-4 times, then one time it stays on, and it says on for 2 weeks or so without shutting itself off yet again. i download a temperature monitor and figure out that the CPU temp skyrockets up to near 80c , then it shuts off. so i open up the side and stick a house fan next to it to keep it cool. I go to my local computer shop, where he replaces the fan and says that its all good, which it was for a couple days. then i notice the fan speed is erratic, 5k rpm down to 1800 up to 7300 down to 800, etc. Computer shop guy tells me, you probly got a bad power supply, so i fix that. also, works for a couple days. Now, sometimes when i turn my computer on, the fan works just fine, other times it struggles to even move. sometimes it fixes itself after being on for awhile and sometimes it doesnt. i have no idea what is going on but i am getting tired of a fan on my desk! thank you for helping