MacBook Pro, black screen but the hard drive is still running
I can't remember the model of my Mac book pro but I bought it in 2011. Anyway I'd just logged on and went on iPhoto and then it completely froze, I could move the cursor on the screen but nothing else, I decided to press the power button then the screen went completely blank the keyboard was still lit and the hard drive is still running, After about 20 mins the keyboard light went off and now the keyboard seems inactive, there is a light down on the bottom right hand corner of my mac but nothing else.
I keep pressing the power button and waiting but nothing happens, it has 73% battery so it's not flat.
Does anyone know what it is or what I can do it would be greatly appreciated, I didn't buy it from the apple shop but will they still have a look at it?
Also my mac was fine but I installed mountain lion just after Christmas and it has become slower.
Thank you
MacBook Pro