1. Unplug all telephones and other devices including any filters from your phone sockets and see if your modem/router will work when plugged directly in to the socket.
   
   
2. Try plugging your modem/router directly in to the master socket, to see if the connection is any better from there.
   
   
3. Behind the master socket there is a "test socket". You can undo the 2 screws on the faceplate and access the test socket. Do not however remove the actual socket or expose any of the BT wiring.

*When trying to plug a router or modem directly into a phone socket without a filter, you can use one of the cables that is normally used for plugging in a 56k dial up modem.

• Check that you have installed your filters correctly.
• Add one piece of equipment and filter at a time so that you can track down exactly where the problem lies.

If your problem is solved at stage 3 and particularly if you were having problems related to a low SNR margin then consider replacing the faceplate on your master socket with a special NTE5 adsl faceplate.
See my page on low SNR for more details.