That is a 20 year old product. I doubt if there is any help available beyond your owners manual. I would try the connection wiring from the transport to the dac as a place to start. Check inside the connectors if possible. Check continuity with a meter if applicable. What kind of wiring (digital input) is used by this unit?

All you have to do is physically press the button to the left of it till the 'operational' light comes on and you are good to go.