Why won't my gradient adjustment layer work in photoshop cs5?

I got cs5 a few weeks ago, and it's been working fine until a few days ago, when the gradient adjustment layer stopped working. When I click on it, and use the gradient tool to adjust the image, the adjustment layer's image on the sidebar makes it seem as if the tool is working, but the effect doesn't apply on to the image and it stays the same. I tried using a gradient overlay instead, but that doesn't let me maneuver the overlay. Is there any way to fix this glitch?