No where near enough info to begin to guess.
Airplane mode can stop it for example.
The most likely place to start though is with your network providor.
Log in to your account with them and see if you have any barring in place. Lack of credit PAG or non payment of PM bills will often mean the ability to call out stops.
There can be loads of reasons why a network stops outgoing calls.
As for the phone. What is dispalyed on the screen, icons etc. Try a screen grab
