For the past couple weeks when playing games on my PC I heard what sounded like a .22 pistol shot but could see no smoke and the PC ran normally. This occured about 3 or 4 times and I just thought no more about it. Last evening I was using the PC and it locked up completely. I started looking for the culprit and decided it was the video, I connected the "onboard" video and it's was O.K. I pulled the Nvidea Video 8600 card and saw the 4 blown caps so it's now history.
If you hear a loud POP, look for blown caps. I knew it wasn't the MB as it's a Gigabyte with solid caps but regular caps on a MB would sound the same if blown.