It seems like you could have low voltage DC missing somewhere. If by turning the function switch, the display does not change to indicate the function like EDIT, MEM etc look on the diagnostic page for the input bit display and rotate the switch and see if you can see a bit pattern changing in the word assigned to the switch inputs.
If you see nothing changing, check the 24v supply to the pendant.
It appears you have a Fanuc control? what model?