Potinara Red Crab, Root question

[Helen]

Hi, I am a first time orchid owner. March 11th I purchased a Potinara Red Crab at a botanical gardens orchid show. It had two buds ready to open, one with a slight black mark on it. The seller told me it was a root plant that he rec'd from Florida and just potted it. After two days at home the buds starting getting blacker and blacker and shriving. My friend suggested re-potting it and to look at the roots.

The roots were all dark and mostly flattened out and thin. I since read that roots should be white...There are one or two white ones near the top of the plant but they are not too firm to the touch and the tips are dark

Can someone please help me? I'd like to know if my plant is dying? or is there something I can do? I repotted with mix of bark, charcoal and some sphagnum moss...I don't know how much to water it, etc.

THank you to anyone who can help me. Hopefully I am worried for nothing!
FirstTimer