How can I get my BT Freestyle 2200 handset to work again?

re BT Freestyle 2200.
One of the handsets does not work any more.
Symptoms are no dialling tone, in spite of being only two feet from base unit. The display shows a row of flashing dots, and a flashing battery indicator.The set emits a faint click about every second. New
Rechargeable batteries, charged up yesterday, have been fitted, but to no avail.

Any ideas, please?