This is really a curiosity as much as anything. It might not be a WinXP-specific issue, it's just that WinXP is the only OS I've tried so far.
Put simply, after booting up I can activate one program (doesn't matter which) and it will look OK until I try to click on it to do anything, then it will become apparent that XP has "frozen".
But it hasn't really frozen. Title bar of the program that was activated/clicked will turn from blue to gray (i.e., "inactive window" color). Mouse still moves cursor, though nothing can be clicked. Keyboard still works and can CTRL-ALT-DEL to bring up Task Manager. This will also appear to be "frozen" when clicked once, but upon the second click it will be fine. After that, everything is A-OK and I won't experience any issues for the rest of the session (even after leaving the PC on for days).
However, this is a very reliable pattern (i.e.: boot > start any prog > click anything and prog goes inactive > CTRL-ALT-DEL > Task Manager > click TM once and it goes inactive > click it second time and everything is fine). Doesn't matter what program I try running at the outset. Doesn't matter how long I wait after Windows has booted. It's not really a huge problem, more of a nuisance, but it's certainly strange.
This started happening after I upgraded a few components (C: was on a new drive which was fully formatted with a fresh OS install). At first I thought it might have been the OS install and I formatted and reinstalled, but got same problem. Then I went ahead and reformatted and tried WinXP 64-bit (figured what the heck, was curious to see how it was anyway), but problem persisted, so now I think it might be a hardware issue.
Thanks for the idea. I run HWMonitor shortly after startup (tend to do this with new builds just to see how things are going) and temps/volts seem stable. I'm not running it immediately after boot, of course. Maybe I'll add it to startup and see if I can get earlier readings, but have not noticed any strange activity in either area after several days of being on 24/7 (min/max stats well within norms).
Also, this happens no matter when I try to run the first prog after booting windows, whether I try to do it immediately or wait 15 minutes. And it only happens to the first prog I try to run, not to any others no matter how many I run afterward. Is that consistent with this heat/power idea?
Regardless, I'll try getting HWMonitor running as soon as possible after boot to see if I can catch a spike.