Will not record an incoming call?

I purchased a BT Synergy 4500 (Quad phone) system in 2007, but have only now needed to use it. Although I can record my personal incoming message and the answer machine element says it is set to record and answer (after 5 rings) the answer machine will not kick in. I contacted Sky who are my provider and they disconnected my 1571 service as they thought that might be the issue but no joy. Similarly the base station ring tone is set to "off"; however, that also rings (a different tone) to the 3 handset melodies. Any ideas? HELP I'M GOING CRAZY - MANY THANKS