Changed modem, one computer goes online, others don't

I changed my modem, virtually the same box. time warner activated it and one computer (Mountain Lion) finds the wireless and goes online. The rest ipad/iphone and other computer running Lion see the airport, show it as selected but don't connect online. When I check airport utility is says internet is disconnected, although all lights are flashing and one computer works. Have tried turning everything off and back on and nothing seems to work. thanks for help.