Download and install the free version of Malwarebytes from
http://www.malwarebytes.org/ then run it, click on the tab to get the latest updates, then run a scan. Have Malwarebytes delete anything it finds, reboot your computer and see if that has fixed the problem.
You could also try superantispyware from
http://www.superantispyware.com/ - there is a free version of it available, and again install, get the latest updates and then run a scan.
Note that these may take a while to complete the scan so be patient or run them overnight or when you aren't planning to use the computer for a while