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I have a kindle 2 aand it has line on the screen,it still powers on but you can't reed the scree because of the lines.

If the lines are parallel it can sometimes be a grounding issue. Try to disassemble the Zune and start it up in partially disassembled condition.
If it works fine like that, remove the grounding lattice behind the motherboard, insulate grounding contacts. It may sound paradoxial, but insulating the grounding contacts will remove that issue.

If the lines are not parallel and the screen looks like it has cracks, you have to replace the screen.