Resposta para "top half of screen is greyed out"I had a similar problem. It was the top right of the screen was darker and steadily got worse. However it displayed fine on an external monitor. Try the flashlight test on it to see if it is the backlight. If the image clears up when you display the light on it then it is probably the backlight. In my case it was the inverter cable.
Resposta para "After house power surge, iMac won't turn on anymore."Dumb question, but you check the power strip? Maybe it shorted out and you need to reset it, unplug it, or plug your mac straight into the wall. I had a similar problem and it was the power strip. I unplugged it for a minute and replugged it and in. That fixed it. This is probably not the fix, but always try the simple stuff before diving into the mac.