Chosen Solution
Replaced the screen on a A12 Samsung and now it flashes and touch screen does not work. You can restart the phone and sometimes it works as it should. When I say flashes the back ground goes from normal to a high lighted screen.
@sunfishsafari double check your work first. Check the cable connector as well as the board connector. Make sure there are not bend pins etc. It is possible that you have a bad screen. This is more common than we would anticipate. I would contact the seller and replace it one more time. Anything else would be related to the video circuitry on the circuit board and would require some board level repair.
