Okay sounds like it might be a heat issue. Simply because when you go into more intensive tasks it shuts down. And larger tasks create more heat.
Your of the female persuasion right? How computer savy are you? We will probably need some detailed specs on your system until we can really help you.
Your right it could be a driver issue. Or a cpu issue. One thing you could do right away is this. Download this program CPU burn and turn it on for like ten minutes or so if your computer suddenly restarts then you know its your cpu. http://users.bigpond.net.au/cpuburn/
Do you play any games. Thats probably the best way to figure out if its your video card.
Anyways just post those specs and I promise we will help you out.
By the way my 25 year old aunt is over in Australia right now. Some college thing. Personally colleges dont teach you a whole lot. Thats why I am a loser and dropped out.