Complete System Lockup- Can you help?

[Ultra Steel]

Hello folks, I have a fairly bizarre issue with my most important and high use PC.

When browsing the web (hence my choice of this forum) my PC spontaneously, instantly freezes. I mean completely- if music or sound was playing, it repeats or drones, the keyboard and mouse "turn off," the screen freezes, and nothing I do has any effect except a hard reset or power button shut down.

This has happened with three (3!) browsers- Firefox, Google Chrome, and IE8. I can do anything and everything else for hours on end- like high end gaming, without incident. This system has been stable (even overclocked) for more than a year, with no serious viral infections; Norton has caught them all before they got their teeth in my system, so far as I know.

Complete Symptoms, Regardless of browser:
-Multiple tabs open (2-4 at a time)
-amount of browsing time varies- its not every 10 mins, or half hour.
-at least 1 web page running flash (Several times- Facebook was active screen)
-click on a link(anything), the following happens...
PC freezes, lights go off on keyboard and mouse. neither responds, even if plugged/unplugged, or plugged into a different USB slot. Plugging in a different mouse also obtains no result.
Waiting 10+ minutes doesn't correct the problem


Here's some quick system info:
Windows Vista with all updates, 2.14 Ghz Intel CPU (Overclocked to a measly 2.3Ghz), 4GB RAM, Norton AV and firewall, Threatfire.
Microsoft Keyboard
Logitech Gaming mouse
All proper drivers and updates.

More things to keep in mind:
-I'm not a tech newbie, I'm an A+ Certified tech working as systems admin in an IT field. (This is really ****ing me off!) Full A/V scans and Threatfire scans turned up nothing.
-Removed all traces of Flash from Windows/Firefox plugins and restarted. When I went back to Adobe to reinstall, the browser crashed again. Have been unable to browse long enough without Flash to rule flash out, because all the place I need to go use flash. End up reinstalling flash after a short time of stable work. But (as seen above) just going to Adobe's flash download page causes system freeze.

I don't think its hardware related, because it only happens when browsing. I do high-end gaming (WoW, CSS, many more) that use far more system resources.

What can be causing this system crash? Any help appreciated.

Thanks

 

[Ste]

This normally has to do with a failing Harddrive or bad RAM or even a bad PSU, but not always.

I would first disable as many un needed processors as possible through msconfig. ( I suggest this for almost anything)

You can perform a chkdsk to see if it may be the harddrive.

memtest for 4 hours to test memory.

a digital multimeter to test psu rails.

May also want to flash bios and reset all overclocks back to stock for the time being.