2002 mercury sable, first ignition cranking but no start.

Could be a number of thing's , can you do automotive electrical testing ? Do you know if starting is PCM / ECM controlled or BCM controlled ? Do you know what these are ? BCM - body control module , PCM/ECM - engine computer !
Moving the ignition switch to the START position sends a 12-volt signal to the engine control module (ECM)/powertrain control module (PCM) Crank Request circuit. The ECM/PCM verifies that the transmission is in the PARK or NEUTRAL position. With the transmission in Park, voltage flows through the Park/Neutral position switch and feeds the starter relay coil. The PCM then grounds the control circuit of the starter relay. When the starter relay is energized it allows battery positive voltage to the starter solenoid S terminal. On some vehicles the starter will continue to crank the engine with the key released until it starts or the crank command has timed out to prevent excessive heat build up in the starter circuitry or the ECM/PCM receives an engine run flag.
Circuit Description (BCM Controlled)
Moving the ignition to the START position signals the body control module (BCM) that engine crank has been requested. The BCM verifies that theft is not active and sends a serial data message to the powertrain control module (PCM) requesting engine start. The BCM also energizes the RUN/CRANK RELAY. When the RUN/CRANK RELAY switch side closes, and the vehicle is in Park or Neutral or with the clutch is fully depressed, if equipped, supplies voltage to the starter relay coil. The PCM verifies the transmission is in Park or Neutral and the clutch is fully depressed, if equipped. The PCM will then ground the control circuit of the starter relay, closing the switch supplying voltage to the starter solenoid. On some vehicles the starter will continue to crank the engine with the key released until it starts of the crank command has timed out to prevent excessive heat build up in the starter circuitry or the PCM receives an engine run flag.
Do you know what a park neutral safety switch is ? What do you mean key stuck in ignition ? Can't turn the key to off position , or you can an the key will not come out ?
Your best bet , take it to a qualified repair shop .

hello my 1993 mercury sable. cranks but will not start.it will not trun over to make it drive.

Verify coolant temp sensor

MAke sure its in park( just move it though the gear shifts) sometimes the neutral switch gets sloppy age/usage/transmission swap etc. Check for voltage at the coil positive terminal when the ignition key is on. YES there is voltage, the problem is on the trigger side of the coil (pickup, crank sensor, ignition module or primary wiring circuit). If there is NO voltage at the coil, the problem is on the supply side (the ignition switch or ignition wiring circuit). Check Relays and Fuses.

When you turn key to `start'' does it seem to be drawing power,like do the lights dim? don-ohio

Probably the crank sensor, do you hear the fuel pump 'buzz' when you turn on the key (not cranking the engine, just key on)? If you do hear the fuel pump (only lasts about 2 seconds), it may be the ignition module, otherwise it is probably the crank sensor.

Check the timing belt

while you state the battery is "strong" what kind of voltage are you getting to the starter solenoid

try running a wire from the + on the battery to the small electrical connector on the solonoid on the starter motor ,turn ign on then use wire to crank engine ,if it cranks but will not start then dealer only in case its the immobilisor

Crank sensor can translate heat. Not allowing restart after the turbo heat radiates in the area. Try a wad of aluminum foil in front of the crank sensor(on the block behind the turbo) . It protects it from heat and its a cheep test. If this works you can make a better sheild or leave the foil.