Open "My Computer"
Right-click on the drive where the folders are located
Choose Properties
Click on the Tools tab
Click the Check Now button
Tick the box "Automatically fix file system errors"
If you suspect a physical fault with the hard drive, tick the other box as well.
Click Start
If the drive is in use (which it will be if it's the C: drive) you will get a message to that effect, and be asked if you want to perform the check on start-up - confirm that you do.
Close everything
Restart the machine