A couple of ideas:
1. Did you click on the plane and accidentally activate "Hide feature"?
2. F5 > on the General tab scroll down to near the bottom > check "Display Outline of Plane".
Thanks John, it was the F5 issue. I tried the show all features thing before I posted. It was the F5 issue. I knew that option existed becasue it was mentioned in class last week, I just couldn't remember where it was.