Displacement Map not working on added PSD layers

Aside from what the cactus said, check the PSD for whether the layer has some "magic" associated like being a smart object or having custom layer styles and belnding options. That may affect how it's processed in AE. You may need to rasterize or get rid of that fancy stuff.

Mylenium

Any chance you could post a screenshot of your whole window?  There might be a setting or a layer out of place we can spot.

Just from your description, here's a couple of guesses:

• Are you sure the new layer is scaled to fit in your window?  Sometimes Photoschop images are significantly bigger than AE comp dimensions.
• Could you be accidentally looking at the layer in the Comp window and not the composition?  It can be easy to click into a layer and not spot that you're no longer looking at the comp.
• If you make changes to anything, do you see the comp update?  It is possible you've had a crash that's only affected the GPU
• You've put the layers in a new comp.  Did you copy over the adjustment layer and displacement texture?  If so, did you repoint the Displacement Map effect to the adjustment layer?  When copying an effect from one comp to another that involves another layer, you have to relink any effects.