There's nothing there that would cause the ringing to stop.
Call buttons are where your internal and external calls will appear. DS buttons call the station associated with the extender ie a DS25 will call Ext 25 . Could you have dialed a code like 53500 or? If you dial 53 plus the group number (ie 500) you can log yourself in/out of a group.A group is where your lines usually ring to.What does the display look like on the phone your having trouble with?