Hi,
Were there any changes made to the computer prior to the issue?
Please follow the methods.
Method 1:
Let’s test the issue in clean boot.
Refer to the link.
http://support.microsoft.com/kb/929135
NOTE: After troubleshooting, revert the computer to start as usual (Refer to “Step 7” from the link mentioned above)
Method 2:
I would suggest you to download and run the latest Microsoft Safety Scanner on your computer and check if it helps:
http://www.microsoft.com/security/scanner/en-us/default.aspx
Note: Any data files that are infected may only be cleaned by deleting the file entirely, which means there is a potential for data loss.