First things I would check for in your case would be the RAM, or maybe the sound card. I have no idea of knowing what causes the crashes but I have had issues with some features on my sound card that causes system crashes in games. This was solved by disabling these features.
I would also try with fewer ram chips, 1 at the time and different configurations to see if one or more of the chips are defected in some way.

System crashes could be caused by virtually anything, the above mentioned things is what I would check on first. I also recommend reformatting the computer and install a fresh clean windows.