Run Check Disk

Chkdsk is a tool provided by Microsoft® to find and fix disk errors.

Start -> Run

In the dialog box type: 'chkdsk c: /f' (no quotes) -> OK

You will then be asked: "Would you like to schedule this volume to be checked the next time the system restarts? (Y/N)"

Choose Yes

Restart the computer (This may take a long time to complete so schedule it at night or at the end of the workday).