i can't figure out whats wrong?

i can't figure out whats wrong with my car. we had it put on diagnostics and the machine couldn't get into the computer. the car hesitates in idle and idling drive it quits. the trani is slipping but thats not the problem. spark plugs are all good so are wires brand new altinator in it and i keep losing power why could that be. im 21 having my first child just lost my job and when i saw that i was able to get my car fixed and it said for free i was amazed. Well, if this is for real it would be the best thing that would of happened to me in a long time. take care richard cyr of 120 upper quaco road,