It may have a gateway address and an admin address. For example 192.168.0.1 gateway and 192.168.0.100 for admin. Most only set 100 addresses. Make sure you have the right address. Usually the address is the same as the gateway either 192.168.0.1 or 192.168.1.1 if those don't work try .100.
If it's an ISP provided router the login user name and the password should be on the back of the router somewhere.
TC