Something is wrong...
 

Roughly two weeks ago, 2 of my dens started failing fast. One of them I am sure is a goner. Leaves (including new growth) rapidly turning yellow and falling off. If if it was just one, that'd be fine, but on one plant the stems decided to yellow up as well.

The only change was that I upped the humidity a little. Have had them for over a year, and they spend the summer outside in a MUCH more humid environment.

It won't let me post a url as a link, or link the images straight up, or attach images so here's the url of what I"m talking about. Sorry for cellphone quality images:

Sick Orchids - Album on Imgur

*** edited to make clickable link to photos *** WR

I can't see your photo. But what are they potted in and what region of the U.S. do you live in?

---------- Post added at 11:28 AM ---------- Previous post was at 11:27 AM ----------

You also haven't made enough posts to post pictures.

The brown looking cane in the first picture, is it soft? Could be rotting if it's soft. When has it been repotted, how are the roots?

If there is rot you may have to cut the areas off with a sterilized instrument and apply cinnamon to open areas on cane. Don't use it on the roots though. The roots might be bad, cut the squishy ones off and repot in new media as needed.
Here is your link for your pics:
Sick Orchids - Album on Imgur

They are in back only. I live in St. Louis. Durring the summer they grew/grow like weeds with our warm shady high humidity. The winter has been a bit dry. They have been find until recently. The only change was adding a humidifier in their area.

---------- Post added at 02:41 PM ---------- Previous post was at 02:38 PM ----------

The brown cane is hard like wood.

They were all repotted last spring before the start of summer, and grew like crazy. They were brought inside about 4-5 months ago when it started getting cold. Problems only started happening less than two weeks ago. The one with the brown cane doesn't have a green cane left. It also never really had roots. The other one, I saw one suggestion to replant in lava rock and water daily? I have a small collection which sit in the kitchen window which are watered daily or every other day.

And fun! I can't even quote urls...

I used to pot my dendrobium until I had the same problem as you. I decided to cut off all canes that were dying and dead roots. Then I just mounted them onto wood or tree fern plaques. They are showing great growth. I have a few dendrobiums in pots but only since they prefer more moisture than most dendrobiums. It seems like that you have a Dendrobium phalaenopsis hybrid which loves a lot of light, warmth, and fertilizer to bloom. If the dead cane was hard but dead, it's probably not enough moisture. But that's my two cents.