Click Start, click All Programs, click Accessories, right-click Command Prompt, and select Run as Administrator.
b. Click Continue or supply Administrator credentials if prompted.
c. In the Command Prompt window type the following, and press Enter:
sfc /scannow
d. You should see the following on-screen message:
Beginning the system scan. This process will take some time.
Beginning verification phase of system scan.
Verification % complete.
e. Once the scan has completed, test to see whether the issue that you are experiencing is resolved or not.
Refer the KB article for more information:
http://support.microsoft.com/kb/929