Add possible overheating to the list. Modern GPU & CPUs will slow way down to try to recover from overheating. But if you are playing a game like FO4 then slowing down won't help. Another possibility is some background process stealing clock cycles and causing the game to get out of sync. A PM type program can decide to call home to check for status updates and cause this. Some update programs will decide to run at a certain time and if the update fails , keep trying. I had this happen with Oblivion on an XP machine. An old HP print driver updater would wake up after the computer had been running for a certain length of time and start trying to call. It was calling an expired update site so it always failed. Then it would wait exactly 10 minutes and try again. Each time it did this it crashed Oblivion. I could reboot the computer and the problem would go away for a while, but until I found and killed that old HP printer update it was difficult to play.