Mercedes won't turn over

My Mercedes would lose power and then
regain it while driving down the interstate.
One day it just would not turn over. I
explain that to the mechanic they took a
look at it and then said it was the crank
shaft position sensor. The car would also
spider like it was having problems with a
clogged fuel line. The crankshaft position
sensor was replaced. After a few tries the
car finally started. After a few hours of
driving, I turned it off. It went right back to
unable to turn over.
  What might it be?  It seems that I will
have to have it towed to a garage and the
AAA guy said that it was probably a fuel
pump that needed to be replaced. He
listened inside the car turning the key to
accessory only (not all the way on) and
wasn't able to hear any sound for fuel
pump engaging.
He had me do the same thing with the key,
turning only to the accessory, while he
listed near the port of where you put the
nozzle in for gas. He said he could not hear
anything and thinks it is not getting any
gas at all.
Any ideas?  Besides, get a new car.

Thank you! I appreciate it.

Wallace