1999 Ford Taurus My car wont start

Engine Mechanical problem
1999 Ford Taurus Front Wheel Drive Automatic 150000 miles

Last week my car broke down on me and for over an hour I tried to get it to start. Finally putting it in Neutral it started. My car is an automatic. The next day, once again, my car wouldnt start. I noticed that the terminal to my battery had broke. So I replaced it. Still nothing. I wouldnt start. I tried again to put it into Neutral but this time nothing. I had it towed to a mechanic and after an hour of sitting there before he could get to it, it started. He said nothing was wrong. I drove it away. Yesterday, once again the car wouldnt start. Mind you, I have full power, Power windows, Power Locks, Power seats, and even lights but the car its~self will not start. If someone could please tell me what could be wrong I would be greatful. I have looked at all the fuses and replaced one out of all of them. Ive tried to jump the car and it wont even take a jump.
Thank you
Kasie