I cannot get onto the internet

Hey, I have a serious problem and I have no idea how to deal with it, I was downloading something for my computer that I needed while in the middle of the download I was attacked by multiple trojan and worm viruses, I tried getting rid of them and ended up with Spyware, the spyware was a rouge spyware known as Contraviro, one of the many spyware taht pose as an anti-virus product. I got rid of it using Ad-aware but after I did My screen acted weird for a moment and then I restarted my computer to fully get rid of the spyware. When I turned it back on and tried to get on the internet it would not let me.. I use Mozilla Firefox and when I entered a page it would not show, it would also not allow me to log into Windows Live instant messenger, Yahoo Instant Messenger, or AOL Instant Messenger. My internet itself still works fine known by how I am still connected to Xbox LIVE on my Xbox 360, but I have no idea how to fix what's wrong with my computer, and am already looking up a new computer to buy. My computer now, that is not working is a Windows XP Home Edition... so if anyone can help me, please do!