Your system probably has some damaged files. To resolve this, run a full CHKDSK:

Click on Start > All Programs > Accessories
Right-click on the Command Prompt entry and select 'Run as Administrator'.
Accept the UAC prompt, after which the Command Prompt window should display.
At the Command prompt, type:
CHKDSK C: /R
and press Enter. You will be told that the drive is locked and CHKDSK will run at the next boot. Press Y, then reboot.
CHKDSK could take a few hours to run, depending on the size of the drive, so don't just sit there waiting for it for finish any time soon! During the process it may find & repair some damaged files (good).
After CHKDSK has finished, Windows should boot normally.

__________________
Cheers,
Paul Edstein
[Fmr MS MVP - Word]