My 1998 Buick Park Ave.

I'm trying to figure out what could be wrong with
my buick park ave. When I got it from my mother I
had to jump start it to get it to start and once it
finally started it ran good started on the first crank
for 3 days then my girlfriend stopped at the store
cut it off and couldn't get it to start back up for
almost 30 mins the very next day I had the same
problem for about 15 mins then it crank up and ran
fine I called my personal mechanic and he said he
thought it could be my coil pack seeing the fuel
pump hums when I go to crank it up and the car
cuts on so the batteries good but it won't crank at
all now I unplugged and replugged the spark plug
wires to the coil pack and it wont do anything now
and the cars dead ! What are some ideas about
what the problem could be and how I can get it
fixed with out investing an arm and a leg ?