Can anyone help fix my BT Synergy 3505 please?

Ok. I Have BT Synergy 3505 Dect phones (outside of 12 month warranty and a present also so no receipt). Theyve been working perfectly until 48 hours ago.

1. No Dial tone.
2. Cant make incoming or outgoing calls.
3. Not the phone line as corded phone works perfectly.
4. All phone symbols look fine. i.e. fully charged in range etc etc.
5. Have disconnected Broadband and plugged base directly into main phone socket that still works fine with corderd phone,(with and without filters).
6. Have tried deregistering handsets and starting again from scratch but no joy.
7. All I hear from the handset sounds as if the phone hasnt been put down after last call, but again line is fine with corded phone and surely deregistering handsets etc would have sorted it if it was that simple?

Any help would be greatly appreciated.

Cheers.

James