Sounds like you might have an infection when you turn on your computer tap F8 until a menu appears, select Safe mode with networking. Open your browser and go to http://www.superantispyware.com/
and download the portable version run it and remove anything it finds.
Then go to http://www.malwarebytes.org/
and download and update it do a quick scan and remove all detections.
After that go to http://www.lavasoft.com/
and download the freeware version of Ad-Aware update and scan remove anything detected.
Then go to http://www.safer-networking.org/en/index.html
and download spybot update it and and scan, remove detections. (Turn off tea timer during install)
Then go to http://www.free-av.com/
and download Avira update and scan then remove any detections.
Now download Revo from http://www.revouninstaller.com/
and use it to remove all the above programs and download Microsoft security essentials from http://www.microsoft.com/security_essentials/
install, update and use it for your main AV.
If your still having trouble come back.