Trying to connect a macbook to the internet.

I have two apple computers, one a macbook pro the other an apple air.

Both will connect to our home and some internet thru wifi.

When away from home we sometimes are unable to connect to the internet using wifi.

One will connect the other will not.

Both pcs' show full wifi connect signals.

I have isolated the problem with the pc's.

I have done the normal checks as per google searches.

Reset the network, forget the wifi connection, rebooted the pc. All to no avail.

We have two iphones and these do not have any problem connecting to the internet thru wifi on the asme routers.

HELP