MacBook Pro :: Screen Freezing While Watching Videos?

i've noticed for a while now that everytime i watch videos on my macbook pro, using vlc player, sometimes the video picture would stop, and or stutter, if it would stop, the audio would go on, but the video remains stop, after a few seconds, before the video would resume, the video would be distort or scrambled for a few seconds before it would come back to normal, it had been happening for some time now, i thought it was just the software, so i tried another player, the mplayer for mac, and it still would stop at random times. but last night, after stuttering for every 10 minutes while watching the video, the screen on my macbook pro freezed. i cannot do anything, but my mouse is movable, and the caps lock on the keyboard still lights, but i cannot do anything but to do a hard reset, it is the first time that has happened to me, the screen freezing, and i don't know if it has anything to do with the stuttering of the video.