My Samsung Galaxy S3 has a black screen Today , i was playing on my Samsung Galaxy S3 and it worked just fine this morning.
After school i trying to play on it and it flickered to a black screen, when i trying to turn it on it powered up but i couldn't  see anything just a black screen and in the corner a blue light to show its turning on( it vibrated also). I could hear sound and i could do my password but i could see anything. Could you please help?
Before it flickered did you see any green light or something. I suspect the screen is cracked. Experienced it twice on my S3. Try to enter download mode, if nothing shows up there too then it probably is screen issue and not some kernel screw up. Also look for some cracks, in my case it was really tough to notice the cracks that caused a large hole in my pocket. 
Best of luck. I wish my inference is wrong.