Weird computer problem! Help, please?

I have a Gateway Model MP694 laptop (it has Windows 7), and something's really wrong with it. I was playing an MMORPG online, and my computer inexplicably shut down (for some strange reason it does this all the time: it does this if I've been on the computer for a long time and roughly every 15 minutes when I'm playing that SPECIFIC game-and it happens faster each time). I'd planned ahead for this, so I had set the game to launch on startup. Though it's always worked before, this time only the taskbar showed on startup, and I couldn't do anything because my mouse wouldn't stop doing the loading swirl. I had to shut down manually, and each time it was the same thing. After about 3 tries, nothing showed up at all! The computer screen was completely black each time, and nothing would load onto the screen. I reset recently-changed options, checked all commonly used programs, and troubleshooted everything I could in Safe Mode, but nothing's working. As of now, I'm asking this question from Safe Mode: this has never happened before and I have no clue what the problem could be. I really need help-if you have any idea what the problem might be or have any clue how to solve it PLEASE TELL ME!