Worried about grandma's orchid

[rannfar]

Hello All!
Recently I inherited an phaleonopsis orchid from my husband's grandmother (she moved into a nursing home and left the orchid in my care). I am completely new to orchids and have been trying desperately to keep it alive. Around Christmas time it sent up two spikes and has been blooming beautifully since then. Here's the problem, recently all of the leaves have started yellowing and developing dead spots and eventually falling off. I know that leaf loss is a natural part of the orchid life cycle, but I'm very concerned since all the leaves appear to be dying. Also, many of the roots appear to be shriveling up and turning brown. There is one new leaf that looks like it may be growing, but i think that one is starting to yellow too. Ive been watering the plant about once a week and keeping it in a sunny window.




Help! Did I just kill grandma's orchid??
Thanks!