Plug into your test socket
To do this, you will need to unscrew/unclip both screws/clips on the bottom of your white Open Reach phone socket. Connect the DSL filter to the test port revealed.
Test your line
Connect a corded telephone into your test socket and check for a dial tone. If you had a noisy line but it is now clear, you can perform a quiet line test by dialing 17070.
Test your equipment
Unplug and then plug back in your equipment piece-by-piece including cabling. By testing your connection throughout, you should be able to identify which piece of equipment is faulty and replace as appropriate.