You have an issue with your harddrive or the boot sector for windows.
first make sure there is no floppy or external drives, thumbdrives etc attached.
Boot from Windows CD to recovery console and run CHKDSK /R
see the microsoft article on how to log into recovery console and start CHKSDSK /R (this may take up to two hours so be patient)
Astrophel capitaltechmd.com tech, February 2009