How to fix the door frame

If you're having the same problem I had, and it's a case of rubbing but the door could be forced closed (so it's just slightly off), I just made a note of where it was rubbing with a bit of crayon (wipes off easily), then took a small hand plane to shave down that area slightly.

Unfortunately, I also made the mistake of passing off the plane to my house mate, who wasn't familiar with its use, and he ended up taking a chunk off of his bedroom door. I have no idea how he managed to do it. So, for using a plane -- you want long strokes, and try to shave the door off -- if it gets caught and starts splitting the grain, stop, move back further, and then lightly shave down past where you had the problem.

1. The loose base is causing catching at the opposite corner because the entire door and frame is pivoting around the upper hinge and nearby framing that is presumably still attached firmly to the jack stud behind the frame. As the bottom left part of the frame swings out, the upper right of the door is moving up to where it hits against the frame there.

2. Take a look at the loose part of the frame and see if the nails attaching it to the jack stud have pulled loose. The hinge side of the door frame is often attached directly to the jack studs (no shims) so securing it may simply be a matter of driving in some brads or finish nails nearby.

   If there were shims behind the frame, they may not be where they were originally; then you'd probably have to remove the door trim to get some more installed in the gap, then drive nails through the door frame, shims and studs.