I have an iMac 2011 21.5 that when you press the power button, the chime sound plays, but nothing is displayed, I tried to leave it there, and the fans go like normal, but nothing appears on the screen, it's not the screen, nor the SSD (I think), because I tried to boot from an external hard drive and, the chime plays, but again, nothing appears on the screen, yet I know that the screen works because, before the problem started, the screen worked perfectly (I didn't dissasemble it) but the iMac normally restarted because of a problem and it became unresponsive, i tried resetting the MLC but it doesn't work! Help!