Dont know what you are trying to connect but if an oldish laptop or computer it may not work if the router is set to 5mgh.
So you have to go into the router via the internet and if the router is set to 5ghz disable it and just run on the 2.4 Ghz.
it may not be that but it was for me. My computer and laptop would not connect to the 5 ghz. Worth a try to see if that is the cause.