The last owner did a lot of home projects, and I've determined that they did a terrible job on just about everything. So keep that in mind here, and I won't be surprised if the answer is "redo everything yourself". But anyway:
I have standard bi-fold closet doors. One side was not hung properly - when the door closed all the way it would hang "low" and the top would easily slip off the track. Eventually the door just fell off the track. I finally got around to re-hanging it and was completely unable. When I put the door back in the bracket on the bottom, the top peg is only high enough to just graze the top bracket. It is simply too short to put the door back up.
I initially assumed that something might have gone wrong with the bottom bracket (a shim moved out of place?) causing the whole thing to lose some height. However, after close inspection, this doesn't seem to be the case or even possible. I looked at the other door (which hangs fine) and noticed that while the fallen door only has a peg on the bottom, the other door appears to have something more like a screw. As a result, perhaps a piece fell off the fallen door when it fell? Its been a few weeks, so if a piece came loose it's probably gone (this is a toddler's room).
Did I lose a piece, resulting in the door no longer fitting in the track? Or is something else wrong with this door? Either way, what is the best way to get this thing hung up again?
Here is the bottom bracket:
And the top bracket. It is definitely a bit loose and has a poorly-executed shim:
Here is the bottom of the bi-fold door, which is just a fixed peg:
And for reference, here's the bottom of the other door, which works fine (and looks like a screw, not a peg).