You should try the old open it up and dust it out first steps. How is all over the web and cheap to do yourself.
After that it gets deep fast.
Running 64 bit version of Win 7 Pro with current updates. Recently have encountered lockups with mouse freezing and pc inoperative - but keyboard remains operative. It seems to occur after pc has been running for substantial durations (2+ hours) and is sporatic. I can only restore operation if I do a power shutdown and restart. I realize there could be multiple causes, but wonder if someone could suggest the more probable reasons for this problem - where to begin and possible fixes.
TIA Frank

Chowhound
Comic Vine
GameFAQs
GameSpot
Giant Bomb
TechRepublic