Snow Leopard problems

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?

GGJstudios said:

If fans spin up without increased heat, try resetting the SMC. If that doesn't help, you may want the Apple store to check to make sure everything is connected properly to the logic board.

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We didn't do that since we had just been to the store and it is packed and a drag to go there with a giant machine (sudden realization of why having the monitor be an integral part of the computer is an advantage: portability when it's broken). We decided to upgrade to Lion which fixed everything. It makes one suspicious about company-generated malware.

GGJstudios said:

There are no Mac viruses in the wild, and no Mac malware exhibits those symptoms.

Mac Virus/Malware FAQ

Click to expand...

From that FAQ, "Like every other OS, Mac OS X is not immune to malware threats, this situation could change at any time, but if a new virus is discovered,..." 1) Just because it's not reported doesn't mean it doesn't exist; 2) Just because it's not reported doesn't mean knowledge of it is not suppressed.

But whether it was a virus or not was not the question, it just acted like one. Anyway, it works now. Thank you for the help!

(Still plans his next machine to be an AMD-based Linux box).