For the last four years I have used a Power Mac G5 with dual 2.5GHz processors as my main machine at home. During this time the machine has been pretty much bullet-proof; it stays turned on most of the time (though in sleep mode when I am at work); the only time it has been switched off is when I have moved house! The one alteration I have made to it was to add an additional hard disk last year.
Last Tuesday without warning the machine stopped - it was not even a graceful shutdown. When I tried to restart it, though I could hear the fans spinning no video signal was generated. I tried the various boot options e.g. single user mode, boot from optical drive, none of which worked. Stumped I went to bed to think about it overnight. In the morning when I tried again, it booted first time. I put it into sleep mode and went to work. When I returned in the evening I started using and after 20 minutes or so it put itself into sleep mode. It repeated this several times until it just stopped again.
I decided to go back to basics so I disconnected all devices except the screen, keyboard and mouse, in case there was a hardware conflict causing the problem. That didn't help. At this point I was starting to get desperate, and concluded that there was probably a hardware fault on the machine. I therefore contacted a local company who are authorised for Apple service, and they suggested I bring the machine in and they could run some diagnostics for me. I couldn't do it until the weekend so I had a couple of days to try to resolve the issue myself.
As a vain attempt to do something useful I opened up the case and was greeted by several thick dust bunnies. There was nothing visibly wrong internally, but embarrassed at the thought of the service engineer seeing the amount of dust in the case, I put a brush nozzle on the end of our vacuum cleaner and sucked out all of the dust. When I looked more carefully I could see that the air ducts onto the CPU cooler (it is liquid cooled) were totally clogged up, so I used the vacuum cleaner to remove most of this dust. Feeling satisfied that I would not deliver a dust-filled machine to be repaired I put the case back together, and tried one last time to start it up.
Hey presto, it worked! That was 4 days ago, and I have not had a problem with it since then. The conclusion I have reached is that the CPUs were getting too hot which was causing the machine to shut down and then to refuse to start up until they had cooled down. I am guessing this is a feature built in to the chipset to prevent permanent damage. I have therefore installed Temperature Monitor so that I can avoid the problem in the future.
It gives a whole new meaning to the phrase "clean down the machine"!