Wireless connected but no internet

We have a dsl wireless modem provided by our ISP that's being used in our boardroom for guests that continues to not connect to the internet but its connected. After a reboot, it'll work but after "x" number hours, or maybe a day the same issue occurs. The lines has been tested with our ISP. Modem has been replaced also. Could it be because we may have too many connections and only allowed "x" number of leases. Also, from the modem, it also connects to a dlink switch to provide connectivity for computers. Any help is appreciated.