Internet Modem Problems?

So.. my internet works perfectly fine when i'm on wireless ( public places) however, i just purchased com-cast. The guy came over and connected my computer to the internet, however, although my homepage is set to google. it will not go to google it keeps forwarding me to a toolbar site it won't even open. I did a spyware check and nothing... The guy said it was a virus but nothing... Does anyone know how to fix this problem?What confuses me is how my browser works just fine when in wireless mode. I would appreciate any help thankk you