The hard disk activity light probably stays on initially...because XP is configured to run a limited (3-step) version of chkdsk when hard shutdowns occur. I myself prefer to then run chkdsk /r (5-step) on the same drive when the system finally does boot.
I would run chkdsk /r on each drive as a first step...and then reboot. I would run the chkdsk /r on the boot partition first, using the XP CD and Recovery Console...then try to boot.
I would then run the chkdsk /r on the other drive from within XP: Start/Run/chkdsk /r, OK. To specify running chkdsk on a hard drive which I've designated as R, the command would be chkdsk R: /r
What error messages are provided in Event Viewer that might be pertinent? EV is usually pretty good about indicating disk problems (once auto reboot on crash is disabled).
Disable Auto Reboot On System Crash - http://www.theeldergeek.com/auto_reboot_on_system_crash.htm
How To Use Event Viewer - http://www.bleepingcomputer.com/forums/t/40108/how-to-use-event-viewer/
If it's something that chkdsk /r cannot repair, then I would move to a manufacturer's hard drive diagnostic.