What you need to do is unplug everything that is connected to the phone cables in your house then plug in one phone that you know will work at the main socket which is usually the nearest one to the front door. if the phone works properly then the fault is elsewhere in your house. If the phone doesn't work, if you have a second phone then try that to confirm that its the main phone line and if it is then phone BT. If the phone works in the socket, you now have a socket that works and a phone that works to test other phones, cables and bit of kit in. Test them one at a time.