I have a mac powerbook g4 and it worked perfectly well until one day it just crashed.
I am not sure why but now when I try and turn it on all I see is a grey loading screen with the apple icon and the sunburst.
It tries to lad for around 1 - 2 and a hal minutes but the just shuts itself down again.
Mine was doing that last year. I took it to the Apple store. They charge a $300 flat rate fix all charge. I got a new motherboard, hardrive (which they upgraded it to the 80 gig) and optical drive. Also threw in a gig of ram for free as well. Basically got a new computer for the $300 bucks