Try this, if it will let you...
Click on 'My Computer'
Right click C: (your OS drive)
In menu click 'Properties'
Click the 'Tools' tab
Under 'Error Checking' click 'Check Now'
click the box next to...
'Automatically Fix File System Errors'
A notice will say it can't do it until the next time you boot. Click 'Yes' and reboot