Automatically locked new layers

Hi,

I've been using PS for a few months when all of a sudden as of this morning, if I open multiple images (JPEG or RAW or text layers), then drag the layer of one image onto another image to make a new layer, once I let go of the mouse I can no longer re-position the layer. The layer isn't showing as locked, but I can't move any layers. I can adjust the transparency and style etc but not move it. This is really frustrating me.