My opinion...it can be a number of things...if you Google that error, you will see a range of opinions that amount to guesses, IMO
If the system had been functioning properly and this happened out of the blue...I would probably change the CMOS battery, if only to eliminate that as a contender.
I might also try the fixmbr command from the XP Recovery Console, if changing the CMOS battery proved to have a non-impact.
And I would run the following command: Start/Run...type chkdsk /r and hit Enter. Type Y in new screen and hit Enter. Reboot the system. The command will execute before booting into Windows. Since you already have had indications that this needs to be done, I would do it before doing anything else...and see if the problems disappear.
Edited by hamluis, 10 July 2011 - 02:35 PM.