Run Malwarebytes AntiMalware first. It is free. (It will say 30 day free trial, but it will continue to work as a manual scanner/manual update after that period.) Then run SuperAntiSpyware, the free version is fine. Remove whatever these two programs find.
Install WOT on all of your browsers.
http://www.mywot.com/
While nothing can keep you completely safe, WOT would likely have stopped you before you visited a bad website where it looks like you picked up a minor cootie.
Finally, run HijackThis and check your results by uploading a log of the results to this page:
http://www.hijackthis.de/
Fix whatever the log analyzer suggests is nasty/bad/etc. But be very careful with this. If you have any doubts, don't bother with the HijackThis part, or have someone who knows the program do it for you.