A reli has my old G4 12" Powerbook. It has been good for years. He complained of blue screen on boot.
So I started it in target disk mode and ran disk utility and disk warrior - no probs found. Then I tried booting the other mac from the target disk. No probs, everything working fine so I concluded the disk in the Powerbook is fine.
Now the interesting bit. It boots in safe mode but a few faint fine vertical lines half an inch long following the pointer around the screen, I checked no unexpected login items.
Next up I plugged in in an external monitor, booted in safe mode again. This time both screens show up fine and no fine lines around the pointer. Then I tried unplugging the external monitor and the jolly powerbook screen stays good with no fine lines. I reboot, and can't back in unless in safe mode. I connect up the external minitor and now I can sometimes boot normallywith the external monitor! Not managed to boot the Powerbook normally without the external monitor, but I can boot with it, then disconnect the external monitor and it is ok?
Is this the video card failing? If so I presume it is part of the logic board and would need to replace that? or any chance it is some bad plist or pref file?