Dead roots? blooming plant, wilted psudobulb, = underwatered?

[Leemoon]

First Orchid Ever and I am going to kill it accedentaly >.< Mystery plant, purchased from the floral department of the local grocery store. Plant has about a two foot stalk, and most of the buds are opened, no camera but here is a scan of one of the flowers, An id on the plant would be immensely helpful I think.
Near daily mistings and watered once a week according to the care card included with the plant, (no species name sorry.) a wilted psudobulb, that I saw when I checked it today seems to indicate lack of water, and when I went to check the roots all the potting medium fell away from being dry. . . I only have had the plant for a week. Most of the roots are white, dry and brittle, and the plant is in bloom, Should I trim the stalk and cut back the dead roots? how can i easily distinguish the dead roots from the live ones. The flower is about the size of a fifty cent piece and the stalk has about 20 to 30 blooms either opened or in the bud stage.

I plan to repot the plant in a combination of pea gravel and orchid potting mix (as I have read that lack of oxygen = death. Help and advice is much appriciated.