won't go into park

My shifter wont go into park. It has a dead stop at reverse, it wont budge at all to go into park. So I had to leave the shifter in Neutral with the E brake on when I stopped the car. Luckily it does start in neutral but I am not driving it until I get it fixed or find the problem. The shifter is located on the floor, not the column, and the other gears do work. It does shift through the others, just not into park.