My PC has been running (mostly) stable for several months now until last night. I have a 2.6 GHz P4, MSI mb, 1GHz RAM, dvd burner, 3 hds (boot is a 40gb western digital), radeon 9800 pro, sb live!, and a hauppage wintv card running Windows XP. I can give more specifics specs if needed.

Here's the list of what happened, and what I've tried. I don't have internet on that pc typically, and as such I only have a firewall (zonealarm) and no anti-virus protection. This weekend I took my pc elsewhere and hooked it up to the internet. I downloaded the SP2, as well as the newest catalyst drivers for my video card. Sunday, I brought my pc back, hooked it up and it worked fine. I shut it down that night. Monday, it started up fine again, and I used it with no problem all day. When I went to sleep, I told it to shut down.

I woke up Tuesday morning, and the shutdown proc seemed to have hanged. It still showed the "Windows is shutting down" splash screen, and wouldn't respond to anything aside from powering down from the power button. I waited a minute to turn it back on, and when I did it gave me an error concerning the power cable connecting my radeon. This has happened once before, and simply reseating the power cable usually works. This time, though, no luck. When I looked closer at the power cable, I saw that one pin seemed to have been scorched slightly. I tried a different power connector, and that error hasn't shown up since.

Now, it boots, and it checks my RAM successfully, and I can enter my BIOS and check the power supply voltages, and they look to be within thresholds (biggest discrepancy is -12.5 V for the -12V level). When it tries to boot into Windows, safe mode is no different, it does one of two things. The white ascii bar will either fill up before it shows the windows start splash screen, and then reboot, or it will hang before showing the white ascii bar. Those are the symptoms.

Here's what I've tried to do. I tried running Windows setup (XP home upgrade CD) and it fails in a large variety of ways. It boots most of the time off the CD, and has crashed in several places as it loaded files, once it errored out saying a file was corrupt (mraid.vbx, or something similar), the last time, it got past the supposedly corrupt file and eventually crashed with a "Trap 00000000x6" or the like. I've also swapped video cards with a friend (and adjusted the BIOS AGP aperture accordingly), and the same happens.

I tried booting off of a knoppix 3.6 liveCD, and it was able to boot once to a prompt, though it couldn't start the x-server, and gave many 'cloop: -3' errors. After I swapped video cards, knoppix gets to the loader, but once it tries to boot, the kernal panics. I think the error is something like "unable to mount vfs at 01:03". I can't quite remember.

My guess is that it is a hardware based failure, but I'm not familiar with how nasty a virus can be, so maybe my pc contracted one. Any help would be greatly appreciated.

When I looked closer at the power cable, I saw that one pin seemed to have been scorched slightly.
Ok, this is really bad. Which pin was it? What color? Is this a floppy power connector or one of the larger molex connectors?

My first advice would be to get a new PSU and hope that fixes things. If not, you've already tried a different vid card, so your next suspect would be the mobo. If it turns out your mobo is fried, I don't think it's safe to use your old vid card anymore, as it probably bit the dust, too.

Well, I'm not familiar with the name of it, but it's the power connector you can use with hd's, so probably molex. Here's my attempt at showing which pin.

Looking at it so you can see the inside of the connector:

/----\
|oooo| <--- leftmost pin was slightly brown/corroded/scorched
------

Here's hoping it's not the mainboard. Thanks for the suggestion.

That would be the +12V rail, and if one of your +12V rails died, that would definitely explain your problems. Buy a new PSU, then download your hard drive manufacturer's diagnostics and make sure it's OK. Then zero-fill the whole thing. You have back-ups, right? ;) Do that first if you wish.