how can i fix my corded phone?

I have a BT Decor 1300 corded phone. there is a problem with the 2 buttons only. These are the Redail/Up Button and Calls/Down Button. These buttons does not function when pressed. I have un screwed the back and checked the cicuit board I cannot find any phsical damage to the circuit board, eveything looks ok. How can I fix this problem.

Thank You.