keyboard interface problem (Denford lathe)

Hi all!
...Trying to enter new program on my ORAC lathe I press (5) to move cursor to <enter new program> line and the cursor blinks under selection(5).
Now if I press (E)ENTER nothing happens. I mean, I am not getting the buzzer tone which verifies that that button was pressed and thus I can not go to the first page of any program as this button(E) looks innactive. Same happens with all 4 data entry buttons located at the same horizontal row. Strange thing here, all manual mode keys respond, and stepper motors spin.
It could be a keyboard interface problem but at this moment I have no idea of where to look at. Could be a faulty IC in the PC1690 (interface board)or may be an accidentally erased EPROM. Who knows.
If anybody in this nice community here ever encountered a similar situation and managed to fix this problem please give me an idea of what to do.
Also, If anyone of you guys have the old boards of this machine and wants to sell them please give me a note here or at <[email protected]>.

regards
http://www.mycncuk.com/attachment.ph...id=15724&stc=1