M6810 Misery -- Virus and Motherboard Trouble?

About 2 months ago my eMachines M6810 starting running slow, then I turned it off and it wouldn't turn back on. A trip to the shop, and 1 new hard drive later I had discovered that they had found a virus (trojan.byteVerify, fwiw) which had corrupted my hard drive, though they were able to retrive all of my data.

I reinstalled XP, from the recovery disc, and immediatelly ran into trouble: pop-up menus were staying on the screen when they should have been closed, the system was running erratically (slow then normal), and finally, it wouldn't shut down, and when I held down the power button for 5 seconds it just beeped one long continuous beep that only stopped after I removed the battery!

Back to the store. They tested all the components, and couldn't find anything wrong, so their conclusion was that it was a motherboard problem, though they didn't test it, itself.

I wasn't satisfied, so I decided to try Knoppix to poke around. Other than taking a ridiculous amount of time to load KDE, I could find no problems, except--the power off problem remained. When I halt, or reboot it shuts everything down, unmounts all drives, etc, and then just hangs. I have to unplug the battery.

For a final stab, I decided to install Ubuntu--this was a mistake. I was never able to complete the installation, it would always freeze during the last phase "Installing packages" .

At this point, I don't know what to do. How can I even find out if the motherboard has problems? I know Ubuntu is not perfect, and I was thinking of trying the latest Debian in a last ditch effort. Anyone have similar problems? Do I risk damaging my computer by pulling out the plug while it's running still?

thanks.

ps - I also have a cracked hinge. I'm really wishing I paid for that extended warranty, of course this happened a month past the end of the included warranty