So it freezes up after a certain amount of time no matter what it's doing?
Well, I suppose a CPU overheat due to fan failure could cause this sort of thing in theory - but I wouldn’t expect this sort of problem to manifest itself so soon after the system is powered up.
Is it an extremely fast processor for which cooling might be more critical?
I remember when messing around with over-clocking a processor a few years ago - it used to take 10 or 20 minutes before the system would freeze up. But that was just with inadequate cooling - not no cooling. On the other hand I worked on an old 486 that ran for months with a seized fan without ever freezing.
Perhaps you could have a peek inside the box to check if the CPU fan is running. This may or may not be easy to check depending on the system setup – the fan could be hidden in some sort of plastic duct connected to the outside world. From the outside it would be hard to hear over the noise of the main case fan.
Anyway, I don’t think this is a likely cause – but it’s something worth checking.
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