Does this error occur every time you restart? If yes, you may want to uninstall steps 2-5 since they did not help with the game.
1) Do you happen to have Comodo installed? I remember it causing back screen issues some time back.
2) I recommend to try reinstalling the graphics card drivers. Maybe the opengl part is corrupted. Uninstall them completely and do a clean reinstall with the latest ones from AMD site.
3) After the reinstallation of the drivers, turn all the graphics to the lowest possible from the launcher and start the game.
4) If the above still don't work, you can try this last thing. Take this file
main_settings.cfg and paste it at Documents\Amnesia\Main overwriting the previous one.