my ibook 800mhz g3 isn't booting up. I just turned it on one day & it showed the apple logo as usual, it went to the Starting up screen, and then it just disappears and i'm left with a blue screen, and the mouse sometimes appears for about 10 seconds and then it goes away. i've tried formatting, installing an earlier operating system, using a boot cd, booting from an external hard drive, everything. i have no idea what's going on. help!