if it is a bug then idk, but it could be a physical issue with the battery not being plugged into the whatamacallit. my iphone 6 had the battery shaking around in it, and it would show the apple logo then turn off over and over. i took it apart, held the the thing that the battery connects to against the battery connector, and tried it again, and it worked. so try that.
if it is just the screen than you can get the screen replaced, and do it normally. but if the damage is more than the screen than you can use a teardown, physically take out the data, and put it in a new phone.