Try re seating the ribbon cables from the DMD controller back the MPU board.
If your DMD is truly dead you will need to swap it or replace it.
If you machine is giving out more that one "bong" you can head over to the pinwiki to get an idea of whats going on.
http://www.pinwiki.com/wiki/index.php?title=Williams_WPC#Power-On_LEDs_and_Sound_Tones_.28Bongs.29