Hi,
Follow these steps and try to test the issue in clean boot mode:
a. Click Start, type “msconfig” in the Start Search box, and then press ENTER. If you are prompted for an administrator password or for a confirmation, type the password, or click Continue.
b. On the General tab, click Selective Startup.
c. Under Selective Startup, click to clear the Load Startup Items check box.
d. Click the Services tab, click to select the Hide All Microsoft Services check box, and then click Disable All.
e. Click Apply and OK.
f. When you are prompted, click Restart.
g. After the computer starts verify whether you are able to resolve the issue.
If your issue is resolved after performing Clean Boot, then follow the steps mentioned in the following KB article to narrow down the exact source:
http://support.microsoft.com/kb/929135
Note: Also, see the section on how to return your computer to a Normal startup mode by following the steps under “Reset the computer to start as usual”.