Trying to upgrade my G5 dual 1.8. Recognizes the cd fine when first put it in. Double click the " install" and hit restart like it says. Upon trying to re-start it hits the gray apple screen and hangs for a couple minutes. Then I get a prompt that I need to restart. Been through this 3 times already. It's not letting me get re-booted with the cd in the drive. Any ideas?