Hello, a few days ago I locked my imac screen and got a black screen with blue lines instead of the lock screen where I usually write my password (pic #2). The only solution I found was to restart the computer but, everytime, it starts up with a similar glitch screen (pic #5), sometime if I'm lucky (1 out of 5 times restarting) it starts up with the same glitch screen but then it displays my user logo behind the blue lines so I can put my password and everything looks normal again (pic #4), but if I lock my screen again (cmd+shift+eject) I would get the same glitch screen as when I restart it. I couldn't find any solution, please help. Thanks.