1996 Nissan Sentra distributor

I've had to replace the distributor four (4) times within the last six months. Using new units not rebuilt.
The car will be running fine, no missing, just as smooth as possible, then it is just like the key is turned off. Nothing else is wrong with the car, just will not fire, turns over great. Put a new distributor in and it will start the first time.
Please help, I've been to several dealers, no one can tell me anything, in fact they say they have never had a problem with the distributors on the sentra's.
Chuck