I've had my pc for eight years, six years ago my pc broke down and would not boot up, instead the pc case red light was on and my pc itself just made a high pitched noise, I fixed this by removing my video card, had no further no problems until last year, my pc began to shut it's self off while playing games like civilization 4 and morrowind about five minutes in to the game, i checked to make sure my hardware was plugged in and also that the temperature was good, and not knowing what else to do I just left it alone until a few days ago, after reading articles about similar issues other people had, I decided to clean my pc of dust, and reapply thermal paste, for three days after that my pc ran great, no shutting down while playing the games I mentioned earlier, however after those three days my pc went back to shutting off five minutes in to the game, it seems that reapplying thermal paste fixed my pc, I still have to reapply again to test and confirm that thermal paste made the difference, my question is this: what is the real problem with my pc, that causes it to need thermal paste reapplied every few days to work properly, and how can I fix this problem permanently?