This is a good site for troubleshooting broadband as well as informative ::. Kitz - ADSL Line + Connection problems .::
and your fault can usually be resolved by changing the microfilter.
You may want to copy and paste that URL into a Wordpad Doc for future ref.
You may want to consider fitting an ADSL faceplate to your master socket if that is where you normally connect your router.
With one of these faceplates fitted you will no longer need any microfilters, but you will only be able to connect the router to the master socket and any extensions then, will be just slaves for a phone.
You can by-pass this by connecting the extension cable to the A & B terminals behind the faceplate to enable its use for broadband, but you will need microfilters on any extension connected that way and it's always best to connect the router to the master socket.
If you wanted to work in another room to the master socket/router but needed a decent strength signal, then by fitting a High Speed ADSL cable of a length to suit, you could have the router wherever you choose and still be connected directly to the master socket.