MacBook Pro black screen - or reset password My MacBook Pro fails to start.
I hear the "ding" sound, the keyboard lights up, but the screen stays black.

After a couple of minutes, I hear the fans growing louder, until after a few minutes, the computer stops.

I tried a few times, also closing the lid, plugging to a TV, options key, etc. Nothing.

Except, once in a while, it seems to start correctly, the screen turns on, and then it tells me I have forgotten my password and offers to reset it.

There is no option to say "NO I haven't forgotten".

When I play along and reset my password, at the end of the process it says my password was successfully reset (including something about FireVault), then it requires me to restart the computer to complete.

Of course, once I restart, I'm back to square one with the black screen. I've managed to reproduce the reset screen 3 times so far - without really coming up with a rule as to when it happens. The rest of the time, just black screen.

It's a MacBook Pro 15" from 2011 (I think), running Yosemite.
This happened to me too with my macbook pro 15 (mid 2012) running yosemite. What I did is took a flashlight and see if there was an image still on the screen. What I found out is that I was able to see the log in screen but it was all dark. After logging in all was back to normal. 

Eventually if that doesn't work you can reset the pram of your computer. Follow this link http://support.apple.com/en-us/ht3964 .