I don't know if it's overheating and turning itself off, or if there's a more serious problem. i had a harddrive problem 8 months ago, and when it was returned the fan ran at full speed, constantly. i took it back to them, and they said the sensor lead hadn't been connected, they did it and everything has been fine ever since. however, in the last few weeks, there have been two days where the mac has just crashed repeatedly, after it'd been on for a few hours. it sits on a glass table, with the vents facing but not up against the wall. if i leave it for a couple of hours, it seems to solve it, leading me to the overheating scenario. it's now out of warranty and i can't afford to have it fixed if there's anything wrong with it, so i'm just wondering if the same thing has happened to any of you?