Chosen Solution
Hi there guys I have here an iPhone 5S that does something rather strange. I have recently refurbed the whole phone with new components, inc battery and screen. The phone powers up, shows the Apple symbol for about 2 seconds then the screen goes blank, however you are able to see the lit up backlight. It stays on for about 15 seconds then shuts down, any ideas of what it could be? Regards Fonebitz
Issue was it just need to be restored through DFU Mode
Try resetting your screen cables connectors and do not have the shield cover for the screen connectors and see if it reboots.
Are you 100% sure all the screws are in the proper holes on the lcd/digitizer bracket? If one of the slightly longer screws is put in the lower right hand screw hole, you could possibly damage your board or put pressure on the board until it behaves the way you are explaining. I have seen this happen personally. I would remove the screws and that bracket. Then Id test it out.
