I am attempting to use a layer mask in Photoshop CS and cannot get it to work. I have reviewed two tutorials and am fairly certain I am doing it correctly. When I apply something [desaturation for example] to the adjustment layer and then click on the layer mask and select either white or black and paint it does nothing. It does not show anything being done in the layer mask thumbnail as illustrated in both tutorials. I have tried to look at the mask properties to see if something is set incorrectly, but dont know enough to determine this. Anyone have an idea?

First thought...what are your brush settings?

Is your brush mode set to normal?
Back hides this layer's adjustment, white shows it.
It's good to start with normal brush mode first to see if it is working properly. Some modes will not work.

Thanks! That had to be it. I tried it again and made sure my brush was normal and the color showed thru.