2007 Grand Prix just up and died. No warning. Fairly new ECM so that can't be it.

My 2007 Grand Prix (my wife's actually) has a leetle problem. No warning to this problem, was running like a champ, was left idling in the driveway for 1 minute and it died. And there she sits two days later.... No one was in the car when it died. Attempting to start the car is rewarded with a brief firing every ten or twenty tries. And a bad smell from the exhaust when it does fire. Two weeks ago a garage in Albuquerque, New Mexico charged me $120 to change the air filter and oil (Synthetic oil that can be mixed with regular oil). The car has 90k miles with only a new power module (ECM) needed, otherwise no problems. Throttle Body has never been cleaned.  Fixes I have tried: #1. Added premium fuel to the tank with a 5 gallon can. #2. Poured an injection cleaner gas additive into the tank. Tank has 9 gallons in it, if the fuel gauge is correct. The gas additive I chose was not the kind that dries up water in the tank or deals with water, instead it deals with injection cleaning.  #3. Disconnected the battery for 30 minutes. #4. Opened up the Throttle Body intake and sprayed starting fluid into the throttle body while having it cranked. (This was one before the battery disconnect attempt). The starting fluid attempt completely failed. It didn't fire at all.  Any advice? Today I cancelled an appointment with a backyard garage mechanic and have decided to schedule the car with the Pontiac dealer I bought the car from, because after researching the net I realized this car is a piece of work when it comes to fixing anything, requiring a PHD in car computer codes, etc...