Move tool

I'm having a problem with my move tool (V) in Photoshop.

I know how to make mini-movies, when I want to put my pictures for the mini-movie part together, the move tool used to 'lock' itself when I moved it, making the layer under and the layer i'm moving be at the same level. Instead of me having to be very careful and guess where they are even.



Does anyone know what the problem is, or how I can get the 'lock' back? I hope someone understands what I'm talking about!