joeeye

I can only guess at a few things to try since I really don't know the system you have there.

Since your saying its dead in the water I'm going to suggest a few things you probably tried all ready, but have you tried the basics yet? like check the power cord by it self? hook it up a meter, then twist it around and bend the cord to see if its got a dead spot in it, or is the 110 volt reading it bouncing all around, or if its even reading like 80 volts? then that will tell you there is a problem.
even check it with an ohm meter for resistance.

Then try checking where the power source comes into the unit if the power reaches there okay and that its a strong 110 volt, or 112, what ever that power outlet is reading. also make sure your wall plug in is okay at 110 volts, because it does seem funny that it went dead all of a sudden.

Anything other than the basic checking I'm not sure what else to say, maybe even giving the motherboard a little bit of a tweeking to see if there is something with it that makes it come on and off, then that would be great to show the customer the board has showed its fault.

I'm suggesting a few dumb things as if the battery it as dead as they come and the customer works off of a power cord, see what the battery reads with the volts?

good luck, let me know what you find, best wishes, Joe