Can an ecu cause your car to turn over but not start? If not, what else can cause my 2000 alero not to start?

Battery, fuel pump, fuel injectors, intake gaskest, o ring, ignition module,alternator, starter all is fine! had oil changes and tune ups on time! I heard ecu is pretty expensive so im trying to go wit other option! im a female and i dont want the guys at the auto shop to take advantage of me! thanx