My wife's iMac has been having strange issues lately. It's one of the 4GB mid-2010 21.5" models, with a fully updated SnowLeopard operating system. -> One day she shut it down and then it wouldn't turn on, not at all. (Yes, I tried resetting the SMC and reseating the DIMMS as mentioned elsewhere on the net, to no avail.) We took it to the AppleStore, and while we were there, he checked it and it still wouldn't boot. While he was writing up a ticket with the aim of replacing the power supply, the machine just turned on and booted itself automatically. -> He ran all the system self-tests and they all passed. We left the system there to have him replace the DVD drive since it stopped working months ago. -> We get the machine home and it begins to exhibit weird behaviour again. The fans seem to run all the time, we checked the temperature using the temperature program available from macupdate, and all the processors were less than 40C. (Usually the fans don't start until 50C is reached.) A week passes and the machine exhibits one other strange behaviour: -> It frequently turns itself off, usually when iPhoto is running Now I would think this is a virus... Does anyone have any similar experiences?