What will cause my 2006 Ford freestar 4.2 L not to shift into any gear.

What is your question?

I had just pulled in about twenty minutes later I went to pull up and turn when I put it in drive and pulled up fine but when I went to back up it wouldn't go in reverse and now it's like it's in neutral.Checked fluid its fine maybe a little over and has been since I bought it used in Feb this year. One other time a month or two ago it done this and wouldn't shift into drive but I thought it was minor because when I shifted to park and back to drive it went. No lights came on it didn't make a noise that I could hear anyways. What could this be?

How long has your 2006 Ford Freestar had this problem?

One other time