Troubleshooting XP STOP:000000x7b errors

The above referenced STOP error recently cropped up on an HP Pavilion 310N. I understand the error refers to inaccesible boot device. But no hardware has been done on this computer since it entered service, and all hardware is installed correctly.
What I need to know (and I have read the MSKB articles but did not find them helpful) is how I put this machine back in service ASAP.

I’ve run chkdsk /r (from XP boot floppy) but that has not resolved the issue.

Any assistance would be appreciated.

David