I had the same problem with the exact same Mac Book Pro model a couple of months ago. With mine, the video flickered vigourously for about 10 secs and then froze. When I tried to turn it on, I got the "gray screen of death" (kernel panic). This is a classic example of a graphic processor failing. Read this article:
http://support.apple.com/kb/TS2377.
You may have to bring it to the Genius Bar. When you're there, insist on testing the graphic processor. I had to go to back to them several times because the guy there insisted that it was the hard drive. If it is the graphic processor, you may be entitled to a free replacement of the logic board even if you're out of warranty.