Question
Just one more little point...I had purchased the below mentioned orchid about three weeks ago and it was in great shape.  I think it is me...do I overwater perhaps also?  I just took the orchid out of the potting mixture and it appears that there are light roots and dark roots (are the dark roots the rotted ones...it appears when I touch the bottoms of the root it some of it comes apart.  Should I snip these?  The roots appear to be about 8" inches or more in length.  The soil is very moist also.  Thanks for your assistance again.  Lorraine
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The text above is a follow-up to ...

-----Question-----
I have purchased quite a few orchids over the years and here is what happens:  The leaves start to droop and sometimes wrinkle.  Also I have had them turn yellow.  Can you tell me if I am over watering or what I am doing wrong.  I water once/week until the medium is moist and make sure the pot drains well.  The plant is in the kitchen and gets fluorescent light and some light from the window nearby.  This drives me crazy as I ultimately have the same problem each time (but the other plants were in different areas of the house).  Thanks for your assistance.
Lorraine
-----Answer-----
My best guess is that you have not repotted your plants in an orchid potting mix.  The result is that you have root rot.  You need to unpot each plant and check the roots.  Remove any "mushy" roots as they are dead and the reason the plant is starving to death.  Once you have removed the mushy roots and cleaned the healthy ones by rinsing them in luke warm water, you can repot each plant in fresh orchid mix.  Use a new pot that will nicely accommodate the remaining root mass (the roots should touch the inner walls of the pot).  If you have had a lot of rot, you may be using a smaller pot than they were in.  While this will not correct any damage that has occurred, it will ensure that any new growth will be strong and healthy.  An annual repotting is generally recommended.

Answer
It takes quite some time for root rot to set in.  It sounds as if it has and you need to remove the rotted portion of your roots. There is no way of knowing how long the plant has been in its current potting mix.  Root rot does not have to do with your overwatering.  Over time the potting mix turns to a soil-like mixture which retains more moisture and leads to root rot. With a fresh orchid potting mix you can continue to water weekly because the mix won't become waterlogged.  Any roots that collapse when you apply pressure between your thumb and forefinger are rotted.  Healthy roots are green and very firm when wet.  Remove the rotted portion of any roots by cutting that portion away from the healthy portion before repotting.