I would agree with AKBray or it may be that your linkage has worked loose. The easiest way to fix or check the linkage is to follow the instructions below.
1. Put the car in neutral (shut off and block the wheels of course).
2. Disconnect the linkage where the rods meet.
3. Put the shifter in neutral.
4. Put transmission selector on the transmission all the way back so the car is in park (it should be in park).
4. Then push the transmission selector lever forward (toward front of car) 2 places-1st is reverse,2nd is neutral
5. Reconnect the linkage and made sure it is properly connected.
6. Put car in park and remove wheel blocks.
For any who are confused on why I say pull all the way back for park, it is very easy. When you pull back on the shifter from park, that pushes the linkage foward into gear. So pushing foward on the shifter into park, pulls the linkage back into park.
By all means check to make sure the linkage is properly adjusted.
If it is adjusted then you have probably broken the Park pawl spring, the Park pawl itself or the retainer could have come off the link.
If it is any of these the transmission will have to be removed to fix it.
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