1) do you see a button with ON or OFF on it ?
it should be ON, if it is OFF, click it to switch it to ON
2) try letting HFS select a free port for you, to do this you just have to leave blank the port box. to edit the port box you will have to switch off the server.
3) if you know how to do it, check if the port displayed in the port box, is occupied by HFS.