I had this problem too. The MacBook would chime and the screen would glow whilst staying dark. This is what Apple Support Live Chat told me to do and it worked straight away: 1) After your Mac is shut down and plugged in, unplug any external devices — like external hard drives, flash drives, or printers. 2) Press (left side): Shift-Control-Option keys and the power button at the same time, briefly, then let go. 3) The computer should remain off for this reset, though you may notice the LED on the charger change colors. Then go right into a PRAM reset: 1) While the computer is still OFF, locate the “Command + Option + P + R” keys. 2) Turn on the computer and immediately hold down these keys until you hear the startup chime twice, then let go. 3) Let the computer start up as it normally would (You should see your screen by now if this fixed the issue).