if you havent already done this, scan your computer for any spywares or viruses. good spyware utilitities to download include spybot and adware se. you can download them by clicking on the links on my sig.
also, i recommend downloading a good anti-virus program such as AVG. download the programs, install them and update them. then run spybot, adware se, and even avg and see if they detect any spywares or trojans.
let the program get rid of the garbage.