car will not start.

I have a 2000 Gallant. I had trouble starting the acr at times. Found a corroded pos. battery post connctor. Change post and jumped car all good. A week later car would not start. So i gat another jump and change the negative post on battery. Jumped car and it started. When i went to take off i put car in drive and it cut off. We gave another jump with no luck. Car would not start. When I tried to start car all i could here was the starter solenoid click. So I changed the starter and still the same problem. So i had both starters tested and the tested good. I had the battery tested and it was also good. I even turned the crank shaft pulley to eliminate a seized motor. Any ideas on what it could be? Need help. Thanks.