I am staying at a friend's house and am able to connect to their wireless internet just fine. But since I connected to their internet, he and his roommate are no longer able to connect with their computers. They are not even able to connect using a LAN line. Is there something I did to make this happen? Any way to fix it. There is an issue still, even when my computer is off or not even present. Please help.

Just you connecting to their wireless network shouldn't have done anything to prevent them from connecting either wirelessly or via a wire. From what you've said, I think the best suggestion would be to reset the router to it's factory configuration and redo it.

Kind of depends on how you and they connect. Might be that his system uses a public ip at a computer. Might be that your old config is actually online instead of his. Look at IP addresses and log on to the modem or router and see the config. Playing to the angels Les Paul (1915-2009)