Having a Problem with My PC

I have been having some serious problems with my PC lately, and I am thinking that the overheating problems could be a lot of different things. I am wondering if perhaps the real problem is in the software, the part of the OS that tells the computer that the hardware is too hot. It obviously could be the CPU fan or perhaps the thermal paste that holds the CPU fan to the CPU has gotten bad over time. I was checking out some blogs like tech eighty to look for an easy solution, but I am afraid that I really need to get a big after market CPU fan that is going to do a much better job of cooling it down. Of course that is pretty easy to talk about, but it is really complicated when you set out to do it. They never seem to have a good set of instructions.

The problem itself is extremely strange to me, because at times it seems to happen repeatedly, every half hour over and over and over again. Then it will not happen for a couple of days, or only happen once in a day. In fact the computer will cut off abruptly. That is not good for a computer, but so far the problems have been minor. The OS has not been corrupt, although one time it did make me do a system restore. That was not a big deal, because I have been expect that would eventually happen and creating save points every few hours when I remember to do it. So I did not really lose that much work at all, only about half an hour in which I had not been really doing anything that was vital. I really do need to figure out how to stop it.