How do I get new roots to grow ?

1. Keep the root zone fairly dry [I don't mean stop watering altogether,
but cut back even further than you have so far]. If your conditions are
cool and dry [low humidity], you may need to do the plastic bag routine
which has been described here many times before, or mist the foliage lightly
but frequently.

2. You can try a root stimulator such as Superthrive or DynaGrow K-L-N.

3. A fungicide treatment shouldn't hurt and might help.

But unless this plant is rare/expensive, or has some special sentimental
value, why not just start over with a healthy, properly-potted replacement
from your local orchid nursery? Chemicals are expensive, pesky to store,
pesky to use safely [gloves, mask or respirator, etc.] -- and rarely
available in quantities that are practical for a person with only a few
plants.

--
Kenni Judd
Juno Beach Orchids
http://www.jborchids.com