2000 Other Jeep Models 2000 Jeep Grand Cherokee wont start

I went to the doctors and came out and the battery was dead. I had someone jump me, and I made it three miles down the road. Then I called a garage and they said the battery was bad and had low fuel pressure, so they fixed it and it still wont start. The mechanic puts the dianogics on it and says everything is a pass. He replaced all of the plugs and coil pack and it stillwont start. Checked the fuel pressure and it has lots of pressure. My garage bill is costing me almost as much as I paid for the jeep a year ago so do you know what it could be.