You may have to change the mode of the images you are working on. Make sure when you open the images you change them to RGB (image > mode > RGB) - this allows you to use all the photoshop features. Also, the easiest way of copying one image into another is to have both images open and visible (window > tile) and use the move tool to drag one image onto the other- this will create a new layer for your new image. Hope this helps. If it doesn't, let us know.