light-fixture
Please check the photograph of the light fixture. All the bulbs have gone out and I cannot get the glass out to replace them. I unscrewed the decorative thing at the bottom. After that I unscrewed another bolt with washer but the glass is not moving. I'm not sure what to do after that. I'm trying to move the decorative thing on top of glass also, but it's moving at all.
I had a very similar light, and the key was this:
Any upward pressure exerted from grabbing the glass created friction that made it not turn.
You want to touch as lightly as you can, near the edges, and try to apply rotational energy only, with no pushing up.
Unfortunately, that is roughly impossible to do if you're reaching so high that you need to press up on the glass to maintain balance. So, you still need to solve the problem of getting higher (and you should NOT climb on anything placed on a bed unless it's highly stable). But if you can get a bit closer, try less pressure, rather than more.
It feels very counter intuitive, but it helped me in a similar circumstance.
One other thing that may help, suggested by none other than @Joel Spolsky, was to try using rubber or latex gloves to allow you to produce more friction without more pressure.
Looking at the geometry, it can only be paint holding it up. I would stay away from any solvents.
I would add a second putty knife, with a stiff blade. Use a slightly larger (wider to distribute the force of the lifting blade) putty knife against the ceiling (and under the lip of the fixture). Put the stiffer, skinny blade between the wide blade and the fixture. Pry up slightly, all around the circumference of the fixture. You will break it loose.
The prybar is overkill (in the photo), but illustrates how to protect the underlying drywall. (Guess what happens if you use the prybar alone. Ask me why I know :-O)
Good plan by Christos regarding leaving the new fixture, though I believe you will succeed removing the original.
Best Answer
The light fixture should have come loose after loosening that nut.
Try the following:
If it does not it could be stuck ceiling due to paint or grime as someone mentioned in the comments.
If this is the case, try being a little more aggressive in your rotation, again being careful as it can slide free.