No Start '94 100S...the common suspects have been eliminated...ideas??

[Cwalln at aol.com]

My '94 100S has been perfectly reliable for the 5 years I have owned it.  Two 
weeks ago, it would not start...no problem turning over...a computer 
somewhere appears to be not giving the ok to start...towed the car to a shop 
great in diagnostics.

No error codes.  The shop has been going through and swapping out computer 
parts from a same vintage, but running Audi, in an attempt to identify the 
problem.  The common suspects, the crankshaft position sensor and the 
ignition control module appear to be working properly.

Before the shop goes the next step and pulls the main and very expensive ECU 
deeply buried behind the glove box...has anyone out there seen this kind of 
problem, or have some ideas on how to find the culprit?

Even the Audi technician at the local dealer is stumped.

Chris W.