1993 347 cobra no spark

First off its a 1990 gt that i put together everything is from a 93 cobra down to the wiring just in a gt body. My problem is it lost spark i backed it out of the garage and shut it off. When i started it up it ran a few seconds and shut off didnt die just shut off. I tryed everything new coil, distributer the whole thing pulled the computer, its all got power. I'm stuck and don't know what to check next.