My 4 door 1997 ford mercury will not start unless i jump it off but it won't crank back up after it is shut off.

Sounds like a problem with the key switch, probably the security system. You may only have power to the fuel pump when the engine is cranking.
Is the security light on or flashing ?

Hi Kevin it sounds to me like your solenoid that is attached to your starter motor needs replacing had this with a ford cortina mk 5

Are you saying the engine will not crank, or not start ?
If it won't crank, have you had the battery tested ? Is it draining power overnight ?

Check fuel pressure at motor with a gauge
& see if it holds

I think the fuel pump has failed,maybe

If it cranks but won't start, you will need to figure out if you are dealing with a spark or fuel problem to proceed.
Check those things and let me know what you find.

Try a slim jim first, down the side of the window. Or AAA or locksmith. If no luck, remove the seat first. Find the screws and bolts around the door handle and arm rest. Most Ford's have screws around the outer side of the panel. I don't believe your's does. The panel lifts or pops off. Once the panel is off, you can reach down and open the door. Just a note. I have done some to where the panel came out in pieces.

Yes, Ford/Mercury dealers have the correct key for it. But your ignition is junk.They'll replace it too. don-ohio

change the soliniold takewire the off one post at a time to change if you get wires mixed up it wont run or crank

Some cars can be reset by turning the ignition to on and waiting a while to reset. Could be as much as 10 minutes. The light will stop flashing when it is reset. Others have a different process. If you have the owners manual it may tell how to do this.

This may work also and a lot faster.
insert the key in
the drivers door, turn left, then right
to disarm and reset it.

This is your Starter and Starter Solinoid. Repace the Starter (Comes with Solinoid) and you will be good to go.