Question
I bought a corn plan about a year ago.  Suddenly it started developing brown segments on the stem.  Then the new leaf buds started coming out brown and limp.  Suddenly all the good, green leaves became brown at the point where they are attached to the stem and started falling off.  Out of 3 plants, I am left with two that I may be able to recover.  I do not know what is wrong !!!

Answer
Hi RS,
  The problem you are describing sounds like stem rot. Dracaenas like Janet Craig, Warneckii and corn plants are very susceptible to stem rot. The most common cause of stem rot is over watering.
Unfortunately once stem rot fungus is present it is almost impossible to get rid of and can possibly spread to near by plants. Especially if those plants are also overwatered.
First, stop overwatering the remaining plants and make sure they are receiving proper care. Most Dracaena require medium, filtered light. A curtain filtered east or west facing window is ideal. Some Dracaenas such as Dragon Trees can do well with some direct sunlight but Warneckii and Janet Craig can not tolerate direct sunlight.
To avoid overwatering you should allow the top 1-2 inches of soil to dry between watering then water until a small amount of water comes out the drainage holes on the bottom of the pot. This method of watering leaches out excess salts that can build up in the soil and harm the plant抯 roots and stem. Never let the pot sit in the excess drainage water. Make sure that you never allow the soil to dry out completely. If the rootball dries out it can be fatal for Dracaena like Warneckii and Janet Craig.
I recommend you use room temperature distilled water. Dracaenas, especially Warneckii and Janet Craig, are sensitive to fluoride, chlorine and other mineral deposits commonly found in tap water. Fluoride toxicity can cause brown leaf tips and brown necrotic leaf spots.

I hope this helps. If you have any questions or need additional information please don't hesitate to ask.
          Thanks
              Tracy