Run CHKDSK /R from within the XP Recovery Console !
Set pc BIOS to boot from CDROM. Place XP CD in drive. Reboot from the CD.
Select the first option R Repair/Recovery Console. Select your Windows partition by number. Usually it is 1 .
Login to XP with administrator password. Then run CHKDSK /R from the command line.
Run it once (or repeat) until it shows no errors. This should clear the "dirty" flag on the disk drive C. Run CHKDSK for each drive on your system.
CHKDSK /R :X
where X is letter for disk drive
References for Recovery Console:
Description of the Windows XP Recovery Console - Article ID 314058
HOW TO: Install and Use the Recovery Console for Windows XP
To exit the R Console, use the EXIT command.