My screen on my MacBook Pro keeps going black

I got my MacBook in September of 2010. It's a 2.66 GHz Intel Core i7 with 4 GB 1067 MHz DDR3. I have had great luck with it, until recently. This problem has been going on since like August now and it's time I should quit ignoring it. For some reason when I am just using my computer normally my screen goes black. Everything seems to be disabled but the keypad still lights up. The only way to get my macbook working again to to forcefully shut it off and turn it back on. Sometimes when i use the mouse a certain way (such as sliding 3 fingers to view other open windows) it shuts off. I have also updated my software from Snow Leopard to OS X Lion. I don't know what could be causing it. I have had some issues sending in laptops before to get fixed but I have a feeling it's going to come down to that. I'm a college student and use my computer daily and being a broadcasting major I need this computer for everything I do. Can somebody please help?