Ok, so the other day I updated the machine in my sig to 10.5.6 through software update. It restarted after installing, of course, and it went through the apple logo screen with the spinning bars. It then went to a blue screen, from which it usually goes to the desktop after a few seconds. But it never left that blue screen. It gave me a mouse cursor I can move around, and it goes from a slightly light blue screen to a slightly dark lie screen and back and forth. It will do this for hours on end unless I force shut down the machine. What can I do? I ran the AHT off the install CDs and all is well there. Can anyone help me? I really need it.