Hi,
I would suggest you to follow these steps and check if it helps:
Method 1:
Try running Windows Update troubleshooter and check if it helps:
http://windows.microsoft.com/en-US/windows7/Open-the-Windows-Update-troubleshooter
Method 2:
Try performing clean boot and check if it helps:
http://support.microsoft.com/kb/929135
NOTE: After you have finished troubleshooting, make sure you put back the computer to normal startup mode as suggested in step7 from the above KB article.
Hope it helps.