Here's an odd one:

Every-so-often my system stops responding to mouse clicks and most keyboard events.

The screen shows that things are still running (downloads and so forth).

The mouse cursor moves normally, but clicks have no effect. If I hit the Start button the menu pops up, and if I hit it again it pops back down - instantly, but clicks don't work, nor do the arrow or any other keys.

If I hit CTRL-ALT-DEL the task manager (I've substituted the Sysinternals Process Monitor) pops up, and shows that the CPU is almost totally idle. (I didn't notice any unusual applications running, either, though I couldn't scroll down the whole list.)

Device Manager doesn't show anything amiss, and the minimal burn tests I've done on the hardware have come up clean.

Any ideas about what may be happening or how I can get more information from my system?

I'm running XP Pro SP2 on an ASRock ConroeXFire-SATA II w/2G of RAM and two WD SATA drives.

TIA

Oh, yes: I've run NAV 2007 and Ad-Aware with the latest updates and done full system scans. Nothing.