Are you sure you're not using your neighbour's or anything? xD
Maybe try logging into your modem's settings to see if it shows any problems, and so you can set the password and SSID (name). Try it if you can connect at all. You'll need the modem's IP to type into your browser's address bar, some common ones include 127.0.0.1, 10.0.0.138, 192.168.0.1 or 172.16.0.0. If none of them work try contacting your ISP. If you need a username and password that you don't know, try admin as the username and something simple as the password like '1234' or 'admin'. If you can connect to any of those IPs then you know it's not a computer -> modem problem, it's a modem -> internet problem.
Also, you can try an ethernet cable (the yellow one) just to see if it works. If that works it means your modem is most likely configured correctly.
Have you contacted your ISP at all?