Dinema Polybulbon - What am I doing wrong?

[Miyuki]

This was supposed to be an easy orchid to grow and bloom. I bought it at a show a year ago. It was mounted on a piece of cork with a small amount of moss. Most of the roots were exposed, and it looked very healthy with bright green leaves and whitish-green roots. Initially I kept it placed in an open terrarium. Since then, most of it's leaves have turned yellow and dropped, and there is no sign of new growth. I took it out of the terrarium and I've tried every location I have to vary light and temperature, and I've re-mounted it with more spagnum. I was hoping some of you could respond by describing your growing methods for these little guys. Any thoughts would be appreciated!