Hi,
Did you make any changes to the computer prior to the issue?
Method 1: I would also suggest you to run “System Maintenance” to diagnose and fix the issue. Follow these steps:
a. Press “Windows key + W” from keyboard.
b. Type “Troubleshooting” without quotes in the search box and hit enter
c. From “Troubleshooting” windows click “View all” option from the left panel.
d. In the list of options, click on “System maintenance”.
e. Click “Next” and follow the on-screen instructions.
Method 2: I would suggest you to perform clean boot and check if the issue persists.
http://support.microsoft.com/kb/929135
Note: Follow How to reset the computer to start as usual after troubleshooting with clean boot from article KB929135 to reset the computer to normal mode.
Hope the information helps. Let us know if you need further assistance with Windows related issues. We will be happy to help.