I just picked up a flash from Circuit City that is a Sunpak PF30x and am wondering if any of you know anything about this flash? If seems like it's not always working like it should. When I go to take the picture, sometimes it will flash with a weak flash. When this happens, the picture is basically a black. The camera that I have is a Nikon D40. Do you think there is something possibly wrong with the flash or is there something that I am doing wrong when using it?