Need photoshop help

Hi, heres my question I hope someone can help with. I have 2 pictures. Both are of a piece of equipment on a white background. Im placing the two different pictures on a new background.

When I place one picture, the white background is removed (good!) but the 2nd picture when I place it on a new page it still has the original white background (bad!). How can I make the 2nd picture have a transparent/remove the background?

thanks alot