My transmission will not shift into drive

I have been having some definite transmission issues. First lost reverse and shifting hard or slamming into second gear. I did some research and figured out that the input shaft nut had came lose. So I got the Saturn automatic transmission service set (socket, some kind of holding tool and the gasket) I got some thread locker red and had a friend of mine watch this YouTube video and fix it. (Tightening the nut) Well all was fine I thought at first because it went into reverse again and started shifting into second like it is suppose to. But, then the next day I noticed that my car will not shift into drive (fourth gear). Transmission fluid is full. Had the filter changed not too long ago. So now I am wondering why will my car not go into drive (fourth gear)? Help!