Elantra won't start and moves when it's in park

Check your input or output sensors on top of tranny. Check engine light?

Rock the car back and forth to remove parking pin from park .

Sounds like you need a new shift cable. Remove the shift cable from the linkage on the transmission. If the transmission linkage moves freely back into the park position and the shift lever inside the car still will not move back into park than the cable is bad. If the transmission shift linkage will not move back into park with the cable removed than the transmission will need to be pulled apart to service the shift rod.

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Most newer models have a safety feature called
shift interlock. This prevents the key from being turned back
to the lock position if you forget to place the gear selector in park.
Depending on the model,
If it uses a cable, it may be sticking or needs adjusting.
If it uses an electrical solenoid. may be blown fuse or park switch.
Tap, shake, and pull up on the shifter and make sure it's in park.

This could be the problem. If your dash indicator is showing reverse but the transmission is in park it could be the safety switch. I'm not talking about the safety switch in the transmission though. In automatics they put a second switch to kill the starter from engaging. You need to adjust the linkage. If your shifter isn't actually on the column but the indicators are there is a cable that attaches the floor shift to the column and that is adjustable. Put the Floor shifter in Park and turn the column section nearest the dash by hand until you find park. Then adjust the cable length as needed. If all you have is the column shift it is still a cable adjustment. Set the emergency brake, drop the shifter to low 1 and adjust the cable linkage by loosening it on the transmission and manually move it all the way to low 1 then tighten it down then move the shifter to park and repeat teh adjustment process to verify that it is properly aligned. Lock the linkage back down and see if the vehicle will start, if it doesn't move the shifter to neutral and try to start the vehicle if the vehicle starts then check the column shift safety switch at the park position to make sure it is still in place and working. Typically, if the vehicle won't start in Park or Neutral it is more likely to be the Transmission neutral safety switch.

It seems you have a defecive stop lamp switch. When pressing on the brake pedal, the switch activates a solenoid in the shifter column to release the shifter 'lock' mechanism.

The car is probably on a steep hill and a lot of pressure is on the park pawl in the automatic transmission. If this is the case, a hard sudden pull should release it. Make sure the brake is on. When parking on a hill in the future use the parking brake before placing the lever in park.

broken cv axle??? were there any noises from the front end when turning for the previous months.

check for the brake switch if this doesnt work wont release from park if this ok then i will check the shifter cable check for power and ground

most likely your brake switch is out. If you had a scanner you would be able to see if the computer see's you pressing on the pedal. Or if you know how to test you could check to see if it switches ( completes the circuit ).