Answer to: iPhone is not booting. Screen flickersWhat model iPhone? The 5 and 6 gens can be damaged by installing the screws in the wrong place causing damage to the motherboard. You would need a microscope to see it. You can search "Long screw damage" or "blue screen of death" (BSOD) to see more symptoms and causes. The only repair for this is highly skilled trace damage micro soldering which very few repair shops can perform.