Seems to be nothing then software, when you boot it does it still have this problem, i mean is there something wrong on the boot screen?
Try to acces recovery, see if it is still there.
Or it may be something hardware related, like malfunctioning gfx chip.
It happened to me with a LG phone (990) . I just replaced the display, but like he said, it could even be the gfx chip. I would bet on the display. In your shoes I would buy a replacement display on **********, the one that I bought for my MI2S costed me about 50 euros and delivered in one month. The second option would be to sell it "as it is" for few bucks.