It doesn't seem possible

If I have to repeat this post one more time I will give up and post whatever is there, mistakes and all.

I think I mentioned that I got a new-to-me camera, a Nikon D200.  I have been trying every setting on the camera to get it to autofocus with every thing the manual suggested, but still no success.  The lens(s)are -AF and should be fine.  So after 2 or 3 hours I was no further along and gave up last night.  This morning I decided to switch out the battery, although it registered about 50% power remaining.  So I recharged the spare (just in case) and I turned the camera upside down to get to the battery in the camera.  And guess what?  The lens fell off the camera and rolled across the floor.  I fished it out, wiped off the bayonet mounts and put it back on, lining up the two tiny white dots.  Ok, now...  And I remembered reading that you had to turn the lens counter crosswise, until it clicked.  It was a little stiff, but I had turned it clockwise when I first put it on; and sure enough, I heard the click as it engaged each other.  And! It autofocuses like a champ.  I didn't tempt fate, so I did not try the other lens, I'll wait until there's future need for that lens.  And I am sure there is dust inside the lens, but that too can wait until I find the little grey squeeze thingy that puffs a little air to blow away the lint/dust.  Carefully.

Now I have to find my list of images recommended, from the Digital Photography Complete Course, if they are inside photos for photogs with a walker.  Wrong phrasing  but you get the drift. 

Several years ago I left my D40 camera on the dining room table all the time, with a glass bowl over it to shield it from cats and dust.  It was there for me or N to use for birds at the feeder, deer browsing, etc.  N told me one day that the camera just kept saying "too dark" and he gave up.  I asked about the lens cover and he said "Damn!"  He had taken most of the same photo classes that I did, and of course every time the instructor said, take the lens cover off.  It is like with computer users that are calling a help line.  They hear, "turn the computer off, wait a few minutes, turn it back on."  To hear the caller have a long pause and then say "turn it off and on, how do I do that?" Anyway... ended up with a lot of nice shots of humming birds.