Operator Panel OP25 ( 6AV3525-1EA01-0AX0)

I have SIEMENS COROS OP25 installed in a factory.
The problem I am facing now is that the left and down arrow keys plus the ENTER key on the front panel does not functioning.
Could any body help me for certain procedure to follow in order to solve this problem.

Your prompt response would be highly appreciated.

best Regards

Salah

Power off
Power on
If OP25 works then
ok.
else
replace it
end if.