Hi Shazia Hasan,
- Did you make any changes to the computer prior to the issue?
- What is the make and model of the computer?
Method 1: I would suggest you to update the drivers for the graphic card from the manufacturers website.
Update a driver for hardware that isn't working properlyhttp://windows.microsoft.com/en-IN/windows7/Update-a-driver-for-hardware-that-isnt-working-properly
Method 2: I would suggest you to perform clean boot and remove the program that is causing the issue.
How to perform a clean boot to troubleshoot a problem in Windows Vista, Windows 7, or Windows 8
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.
Post us the results once you try the above steps.