Cannot Connect to the internet

I have a friends dell optiplex 170L and I cannot get it to connect to the internet. When I received the PC It had the red shield or red circle with the white x and was getting all kinds of pop-ups. I ran AVG free edition and superantispyware and it removed the red shield and the pop-ups. Now I cannot connect to the internet. I have Installed another Network card, and still no internet. I have installed a linksys usb Ethernet adapter and I even Installed my verizion air card and still no internet. The Status say that I am connected, but when I click on internet explorer I get page cannot be displayed and if I click on firefox I get a blank page. PLEASE HELP