Click on the Start button, select Computer, click on c: >> Program Files
In the Program Files folder, rename the folder Windows Defender eg. windows defender.old
Install ccleaner and clean temp file, repair registry
Install Hijackthis and clean registry
Install Spybot Search and destroy and clean your PC.
Note: Please back up your computer before doing above steps. Using of HijackThis is for expert user only. You may loose your running service.