06 Lincoln Town Car will crank but not completely start

I have an 06 Lincoln Town car it was
starting fine needing the occasional jump
(old battery) it will turn over all day but just
will not catch. We replaced the fuel filter,
and the fuel relay in the fuse box under the
hood. The fuel cutt off switch is in the on
pisotion. Can hear the pump trying to
activate when the ignition is in the on
position. What else should i trouble shoot?
My husband read some where if you spray
starter fluid into the intake and it starts its
the fuel pump. We did this it still only turns
over an won't start. What else should we
check? Could it still be the pump even if we
hear it kicking on? Any advice would be
greatly appreciated... I can't even get to
work!!