From: Computerpilot on 01/13/2003
Typically, this means that your computer is having a hard time booting to the primary hard drive. Typically, this is the case with Windows XP or 2K.
I would suspect that your hard drive may have failed or is not properly cabled/jumpered. If you have not recently opened your computer, you might consider running a scandisk on the primary hard drive. If you recieve multiple errors on each scan, you can assume the hard drive has failed.
As a final note, it is possible that the boot sector of your hard drive has recently been damaged. Installing another operating system or 'ghosting' software can cause this to occur. You can repair a master boot sector in the command prompt of Windows repair.