lol..
cool down a bit,
When was the last time the computer was cracked open and thoroughly cleaned, this problem sounds more like a heat related issue then anything, and if you pc hasn't been completely cleaned out within the last 6 months, there is a good reason why it's getting hot and crashing like that.
Also consider that with the number of things that are out on the net and infecting machines, you may want to do a very thorough virus scan, and spyware scan if you can, and start eliminating startup proccesses that you never use or don't need to startup emediately.