which is "mostly" caused by a bad solder joint around the Graphics chip.
You might find that if you press on the left side of the wrist rest, the lines go away.
Sometimes not and eventually the MacBook fails to boot correctly.
You may find somewhere that can reflow the solder around that joint but, as you have already found out, Apple does not do any work on those machines.
Best bet is an Apple Authorized Service Provider, not the Apple Store.
P
We have several vertical lines from top to bottom on a Macbook G4 screen. I assume these are dead pixels.
Is there any way to get this fixed? All I could get out of the 'genius' at the Apple Store was 'we don't support that computer anymore'.

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