The following on Win XP (pro) SP2 up-to-date.

I was working with probably a dozen applications open and all was fine.
I went and tired to do a SnagIt capture (had done many earlier) and the application 'froze', though other applications were still accessible and seemed to be working.

I got to where I needed the capture that was frozen, so I decided to "End task" on SnagIt. There were 2 of them running - the base program and the (attempted) capture.
Neither would stop, though eventually they seemed to.
Trying to restart SnagIt didn't do anything. I'd click it in the Programs list but nothing started.

So I decided to shutdown (restart) figuring that a reboot would solve all.
However, no matter how many times I clicked on Shutdown (which did produce the dialogue each time and the screen did do its greying thing) and then either "Restart" or 'power off', nothing happened. So I ultimately hit ctrl+alt+delete several times, waited a few minutes, then powered off.

When I powered on a message was displayed that Windows has trouble last shutdown and asked me what I wished to do. I first tried 'start normally' and the Windows logo screen appeared momentarily, then a self-reboot.
Then tried 'safe mode with networking'. This time a long list of module names was displayed on the screen (probably hundreds) but then that stopped and another self-reboot.
Same thing after specifying "Safe mode".

I tried remove RAM, even though POST was OK, but no joy.

The system has a RAID1 (mirroring) C: drive, if that matters. I'd remove a drive one at a time if I knew how.

Any ideas as to what might be wrong here? My sense is that the HD has access problems, though I had no warning of such and have no way to confirm. I'm guessing based solely of not being able to boot INTO Windows.

Any ideas appreciated.