My late 2013 iMac 27" LCD backlight stopped functioning. Two weeks ago I installed both memory and a 2T SSD. All were functioning properly until today (used daily). I am currently using the computer through airplay on a separate monitor. I believe that would indicate that the hard drive, memory and logic board are functioning properly. I have reset PRAM/NVRAM and power management. In all conditions and restarts I am able to see video on the screen (with external light) but there is no backlight. (not even a dim glow) What do I need to do to fix this computer?