Not sure what's going on..

On my other computer when we turn it on the moment it connects to the internet the darn thing goes wonky. It starts opening a lot of Explorer windows but they all say something about being unable to connect to the site. I am almost sure it's a virus but I'm not sure how I can do anything when ..I can't even get the computer to stop spamming me! Please someone HELP ME. I don't care what I have to do. Even if I have to redo my system.