I have a question.
How many modifications have been made to the electrical system.
(on your DSM)

I have helped a number of people with no start problems on DSM's
most of the times it is a bad ground. or a ground not hooked up / forgotten about in a rewire. probably not your case because it was running.

i need you to think out side the box... for example i have gotten 3 or 4 DSM's to run were the owners were left frustrated and I boasted I would have it running in 30 min or less.(I also new the car though to be in sound working order) case of beer if you can do it buddy is what they said =)
I found out there power wire for there fuel pump was not making my probe light glow.. thing is this fuel pump rewire was a new and well done mod but i find with the stereo wire 12 gauge it has a million little thin lines of copper all knitted together so any kind of load or draw on them those little fibers some times turn to powder thus good buy good ground or connection.

fixed a 700 HP dsm in under 15 min with and Allan key and razor knife... also noted the car was rewired with a distribution block on fire wall. <(o.0)>