iMac Sporadic Crashing

If the crashes are particularly random, I would look at replacing the memory first when it comes to hardware. Also, make sure that you have at least 2 GB of memory if not 4 for that computer. The next piece of metal to look at replacing would be the hard drive, particularly if it is making any strange sounds. I'm not sure why a the video card and power supply would be replaced for intermittent crashing unless there were some other symptoms that were eliminated. It would be interesting to see the work order on this one.

It it is a software problem, there are many steps to take to isolate the problem. These steps are well documented, so I won't try a brain dump here.

How much memory do you have and which OS are you running. Any special software that you are running?

Step 1- Make sure you have a good backup, intermittent lock-ups may indicate imminent, catastrophic drive failure

I'm running OS X 10.6.4 /w 2 GB 800 MHz DDR2 SDRAM. I have stress tested the memory for a good 3 hours the other day, made about 7 passes without any quantifiable abnormalities. I believe I ruled out a software issue by reinstalling the OS.

Not sure if I am allowed to upload pdf's, but here is a scan of the work order. Not really much information there. He didn't give me any info when he gave it back. Only told me that it was ready to be picked up. I have copies of the kernel crashes, if you'd like to take a look. So far I've only saved three however.
scan.pdf

Losing the drive is not a problem. This computer is used as a remote terminal with a few local tasks. Word processing, internet, email, calendars, and such.

That was actually one of the first pages I read and tried before reinstalling the OS. One of the first searched in goole too. Thank you. (:

Download and install the freeware SmartReporter:  http://www.corecode.at/smartreporter/

It checks your drive hourly for hardware problems.