Daughter has 2000 Grand AM that has been shutting itself off while driving down the road. Prior to this the Service Vehicle Soon light had been on, but was off when it died. Unable to restart car. Waited approximately 20 minutes and then tried it again. Towed the car home and couldn't find anything electrically wrong with it. Started back up. Drove about 5 miles with cruise on and saw the tach drop off to zero. Tried to restart it and it turns over, but the engine won't fire. Towed back home again...by the time got it pulled back up on the dolly with a come along, it started. What do I do now?