Network missing since someone else connected

We have a Belkin wireless router and have never had a problem until tonight. My brother visited and tried to connect to our network with his laptop. He was prompted to enter the number off of the side of the router (not sure what it's called), and he connected fine. However, as soon as he connected we were kicked off on our MacBook. It is no longer even finding the network at all. He disconnected his computer from the network, but it is still missing on our MacBook. Please help if you can! Thank you!