I have searched through every bit of information I can find and I can find nothing on my specific problem. I fear it is just my monitor going out. It's simple. As I increase the brightness on my iMac 27" mid 2011 the display begins to flicker. The flickering accelerates as the brightness goes up ending with a completely black screen at full brightness. Levels 1 2 and 3 are all fine with no detectable flickering.