Hi,
How long have you been facing this issue?
I would suggest you to scan your computer for virus and check if it helps, it might be a virus issue.
You can also try performing online complete PC virus scan on your computer and check if it helps, here is the link:
http://onecare.live.com/site/en-us/default.htm
Please respond back with the status of the issue and let us know if you have any issues.
Azam – Microsoft Support.