Make sure the breaker to the lamppost is off. Check the socket at the lamppost for power. If the socket was damaged it is very possible the problem is at the socket. You may not have to dig at all.You need a meter to check for 120 volts from black to white with switch on.If you have power at socket connections the shell is probably bad and will have to be replaced. That is best scenario.Check there first. Make sure breaker is off.Expose conducters to make test. Turn breaker on. See if you have voltage.