need help

I have a 95 Ford Windstar LX. I can crank up my van, but when I try to put it in gear it won't engaged. It won't engage in any of the gears. What could this problem be?

Is transmission full of fluid? Is the linkage going to the transmission intact? Are the little bolts in the bottom of shifter tight? Is the shift tube broken? Sorry for the questions, but I have run into each of these at least once.

There is also a switch on the transmission....that the shift linkage connects to....often called "neutral" switch....This tells the transmission the position of the shifter.
It is at least partially working, as you can start the car......so It knows that you are in Park/or Neutral.....
The transmission is electronically controlled.....so the switch tells the electronics what gear you have selected, and controls the transmission based upon that.
Let's hope it is one of the things mentioned in this and Way2's post. They are cheaper fixes than many other possibilities....