I've been having problems with my pc for a few weeks now, during games like Minecraft or World of Warcraft, but not with games like Peggle on steam. The issue is when I am actually in game not on login screens, after a short period my CPU usage will jump to 100% and the computer will become unresponsive. Playing minecraft the problem does not occur until after around 5 mins of play but on WoW it's after a few seconds. At first only the game freezes, then shortly the mouse begins to freeze and the rest of my pc, and it will take several minutes to ctrl+alt+delete the process, after which my pc returns to normal. If I don't terminate the process quickly, my monitor will then turn off and go into power saving mode, and I cannot switch it back on without a system reboot. I have ran virus scans, disk defragments, system restores and even re-installed windows and it has not fixed the issue, which lead me to believe the problem was hardware related. After a few checks I am fairly positive the problem is my graphics card, which is pretty old (Nvidia GeForce 6600 GT). I came to this conclusion after slotting it into a different pc that was running fine prior to using the 6600, and it caused the same problems, only with a slightly delayed effect. My question is, can anyone give me a definite diagnosis on the problem, and if there is anything else I can do short of replacing the card to fix the problem?