Pontiac Repair: 1996 Pontiac Grand Am SE, gas millage, insignificant problems

Question
I have a '96 pontiac grand am se that is automatic, with a twin cam, quad 4 engine. It has right at 150,000 miles on it. Got great gas millage with insignificant problems (battery altenator, recalled ignition). The car will not start. The diagnostic machine showed 3 bad sensors all were replaced and it still wouldn't start so we took each back and retried and it still will not start. The timing chain has not broke or lost time, the head is good, the valves and gaskets are good, the electrical system shows its good. The computer is fine. It tries to start, but won't turn all the way over. Also, the injectors aren't clogged or anything. The fuel pump, filters and lines are also good. Do you have any idea what else it could be, the local GM mechanics are stumped. Thanks for your help.

Answer
What do you mean by "it wont turn all the way over"?
Does it crank but not start, or are you having a problem with it cranking? Also what sensors did this so called diagnostic machine say were bad? Are there any codes stored in the computer. There is no such thing as a diagnostic machine. There are some junk tools out there that claim to diagnose cars but if they worked then I would not have a job. Give me some details about what is going on with the car and maybe I can help.