Drag and Drop no longer works

I have been trying to move/copy files by right click and dragging and dropping (using “Explore” on the start menu in Win2k). This used to work fine, but for some reason whenever I try it now, this function is just not working, so I can’t move or copy any of my files…I have tried with many different file types but I cannot do it.
Does anyone know what the problem might be?