No connection?!

[#1]

Hey, I've been having a weird problem with my broadband connection. Can somebody please help?
Normally don't have any problems with connection but very occasionally the router just won't connect at all. When checking the status it goes through training, channel analysis but never gets to showtime. I haven't changed any settings so I don't know why it isn't working. It sometimes works if I pick up the phone and dial 1571, listen to the messages and hang up. The filters are placed in the correct locations. Any ideas????
Cheers

[#2]

Have you tried using different microfilters and connecting using the test socket behind the master socket (assuming the socket is the type with removable faceplate)?  Using the test socket isolates your internal wiring.
Do you have a Sky+ digibox connected to the phone line, and a filter on it?