My car was at the store

My car was at the store. I started, Backed out of my park & it died. Restarted after finally after multiple engine turns, drove a few yards then died again. I did this 3 times then parked. Got it going again and got home fine. Later I restarted it, went great. Next day was taking it to garage to check the problem and it did the same thing multiple times. Got AAA to take me to garage. Mechanic says there is nothing wrong with my fuel system. He has replaced the computer to the spark plugs and the fuel pump & now tells me it is my main computer? They were tracing the wires as they said they had no equipment to test my model. I am a bit sceptical. Any ideas or help as the $ are mounting up?