New build - apps crashing after 1 month...

I built a new pc about a month or so ago and up until last week everything was great. I am using an ASUS M2n-sli 590 motherboard and an AMD 6000+ cpu and 2gb of crucial Ballistix memory. 500gb WD Sata HD. After I built it I bought Everest and let it run for a couple days on stability test mode. No problems. All of a sudden over the past week my apps have started crashing. Even stuff like McAfee and IE7. Even Everest hangs sometimes. I've run a number of different anti-virus scrubs, but nothing really showing up. Sometimes Everest will stop with a message "hardware failure detected - test stopped". However, I can't find any indication within Everest about what kind of hardware failure it detected.
I'm running XP Pro, and at one point things got so bad I ran a repair using the original XP disk. Then things got really crazy and I couldn't restore back to before that. It seems that the "repair" copied over all XP modules, even those that were older than what I already had installed, so now my XP modules are out of sync. I saw a blurp on MS web stie about this problem. After a long time I finally got all the XP modules/upgrades reinstalled and my sytem is running "fairly" stable now. IE7 still goes down periodically for no reason and doesn't wanna run anymore, and the system reboots itself periodically.

Any ideas? Anyone know of a good hardware diagnostic tool? I've run chkdsk and WD diag utilities as well as memory tests, but nothing shows up. I thought Everest was a Diag. tool, but I see nothing of that nature so far.
John in Pa

Have you updated to SP3? If you have a mismatch of windows files like you said, it might be a good idea to run sp3 update. If no relief after that, format and reinstall, then make an image of your clean install to a different hdd or external hdd so you can restore to a known good state if this happens again in the future. Ghost+externalHDD=peace of mind.