Typically, if you have a original EZPATH 1 (as you did not say EZPATHS or SD or 3), there is a set of plugs on the back of the CRT to facilitate the use of a full size keyboard.
If it still has the original mother board, it had a ni-cad battery to maintain the CMOS. It may be dead or may have gone bad (be careful it may leak and destroy the mother board).
The machine has to be left on for a period of time to charge this battery and the CMOS needs to be set. Including shutting off the keyboard test as the half size keyboard will throw an error. It would be rare to see a original mother board as it might be 16 years old.
Because of the uncertainty of what may be inside your machine, I cannot be more specific.
George
(Note: The opinions expressed in this post are my own and are not necessarily those of CNCzone and its management)