Lolipof, the white roots are NOT completely dead! Do not trim any root unless you are 110% sure of what you are doing.
Your orchid is a Phalaenopsis and the leaf is yellow because of too much light. Phalaenopsis do not need any sun, just some what bright light like an African violet might require.
You have come to the right place, "the Orchid Forums" in order to get good information on how to grow them. Please read through all of our 'stickies' and threads because there is so much good information to be found within.
Your leaves are getting soft because the plant is not getting enough water. Why? There may not be enough live roots there to support it. Dead roots are chocolate brown and pull easily away from the rest. Roots that are creamy color, light tan, gray or white are still alive.
If you repot the orchid and get it into a proper sized pot with a good growing media, it will recover fairly quickly. You will see new roots develop in 4-6 weeks, maybe 6/8 but it will recover. With new roots, the strength to the leaves will return.
Scroll back several pages within the forums and read every one you can find including the sticky on Growing Supermarket Orchids-Phalaenopsis!
They will begin to make some sense. When it is in new media, it needs to be watered once every five days. Fertilize 4 times a year. Very weak solutions though.
IF you have any questions feel free to contact us again and feel free to contact me directly via tree mail!
We are so happy that you have found us and it is not hopeless!
