Firstly try this:
Download and run Spybot S+D from
security.kolla.deDownload,
Install,
CLOSE ANY INTERNET EXPLORER WINDOWS (this is important as it cannot fix all of them otherwise)
Run,
Choose "search for updates" (there will be some),
Install the updates,
It will probably restart at this point.
"check for problems".
Fix the selected problems (it will highlight them in red).
It may offer to run the next time windows loads - this is normal and means something was in memory which cannot be fixed at the moment.
Then choose "Immunize" and select "immunize" from the screen that appear. Also worth installing the browser helper from the same screen.