As someone who has now fixed a total of three -- yes, three -- door hinges, I now share with you the secrets of fixing a door hinge that refuses to remain fastened to the door. It requires only one person and takes about half an hour.
What you will need:
- A screwdriver (probably a Phillips-head, but look at the screws)
- Several screws that fit the door hinge (Note: you may be able to reuse the old screws)
- A hammer
- A small block of wood, preferably wedge-shaped
- A few golf tees
- A saw (maybe)
- A level
OK, first off, let's take a look at the hinge. Is it complete? It's no good if you're missing the pivot. This isn't "How to make a door hinge if you're missing parts". I'm fixing an existing, intact one's relationship with the door it serves. OK, it's complete. Is it still in a normal, door-hinge shape? If so, this is a good thing. Leave it alone. If it's not, you're either going to have to reshape it (hopefully with just a hammer), or buy a new one. Go ahead and do that. I'll wait.
OK, so you've got your normal, door-hinge-shaped hinge. Next step is to look at the door. If it's a wood door, we can continue (Because I don't know how to fix a metal door. You probably need a blowtorch and some solder or something). Anyway, we need to look at the door and find out why the hinge doesn't work. Most likely, wear and tear on the door has splintered the wood, loosening the hold that the screws have on the door, and causing them to roll around in the screw-hole uselessly, or fall out altogether. The same thing may have also happened to the door frame. This is OK. We can fix it.
Put the block of wood under the far end of the door, and use the level to ensure that the door is parallel to the floor. We do this for two reasons. One, if the door is off just a little bit, when it's fully opened or closed, it's going to be off by a lot -- it may not even open all the way. Two, if the door is hanging on one end, gravity's going to pull everything downward, making things falsely tight and generally making our lives miserable. Center the hinge where it's supposed to go, and insert the screws. If they hold tight and fast, and the door doesn't slip when you remove the block, the door is fine. This is probably not the case. If they slide in and out easily, or don't hold, they're too loose.
Take out the screw and rotate the hinge out of the way (and put the block back under the door and level it). Take a golf tee, put it in the hole, and bang it in with the hammer. Some people also recommend smearing the tee with wood glue, but I find this unnecessary. If there's still golf tee sticking out (and there probably will be, unless the door is really thick), you'll have to find some way of removing it (e.g. the saw). Once you get a golf tee banged into each loose hole, with none of the tees sticking out, put the hinge back against the door and put the screws back in.
As you turn the screws back in, they'll go straight into the golf tees. The tees will splinter, forcing them tightly up aginst the screw-hole. Tighten the screws as far as they'll go, then remove the block. The door should remain level. Move the door all the way along its pivot. Does it maintain the same distance to the floor throughout? Excellent. Job done.
Truth be told, there are probably a dozen or so other things that could cause a hinge not to work properly. But I haven't seen anything yet that couldn't be fixed this way, except for doors or hinges that needed to be completely replaced. But if that's not the case, /msg all of your door hinge repair questions this way, and I'll follow up with solutions here.