hey i have an i book g4 running tiger that will not boot up, i took it to the apple store last night and they reinstalled tiger on it and it booted up but after 10 min at home with it the computer frozeand i restarted it and it never booted up. it stays on the white screen with the apple and the spinning circle for about 20 min then it goes to a blue screen and will stay there. i have tried reinstalling tiger at home and the apple store and nothing, any ideas? thanks