Chosen Solution
My husband bought his iPhone 6s Plus in July 2018 new from Walmart. He dropped it at work and got the screen replaced somewhere in NY while traveling for work in October or November (it took the guy about 5 minutes to replace the screen). By December there was a dark shadow in one of the top corners, then by January the screen stays completely black with the acception of a weird half lit white streak down the middle of it. We got it to work normally for a few hours by holding the start/ volume up/ home button for a couple days but now it just stays black but rings and seems to work normally other than the display issue.
You can try and replace the screen. It may be something board level because the guy who fixed it last could of fried the backlight or lcd circuit with needs board level repair.
