Start up problems with my '96 Ford Taurus !!

I am facing some weird startup problems with my '96 Ford Taurus.

I bought the car recently and it was working fine. I gave it to the mechanic who did a lot of servicing and it was working better after that. I replaced the battery and got a new one installed. After 2 or 3 days the car started acting weird when i was trying to start it. It just didnt start. I asked my mechanic and he couldnt diagnose much. While i got a towing vehicle to get it to the mechanic , the car suddenly started. Though it started i sent it to the mechanic just to diagnose the issue. After keeping the car with him for 3 days, he couldnt diagnose the issue. The car was starting just fine when it was with him. I brought it back and it seemed to work fine. Today, i faced the same problem again and I am not sure what to do. The engine is cranking fine but its not starting. Infact i had driven the car in the night and it was running perfectly.

What could be the problem? PLease help!!!!

Need to know if it is missing spark or fuel when it will not start. Next time there is a no start, have an old plug and install it in a plug wire and lay it on an engine ground. Have someone crank the car to see if there is spark gouin through the plug. If there is spark, you probablyare missing fuel. If there is no spark, the grank sensor or coils are the most likely items to fail.

could be your fuel pump. check that. of course it a an expensive part.