Dell Inspiron 1501 Screen is veryy extremely dark

Ok I have a Dell Inspiron 1501. I got it for a christmas present brand new last year. It has been working fine until tonight. My daughter hit the power button which made it either hibernate or sleep and when i finally got it to restart the screen was so dark that i couldnt see anything. I pluged it into my external monitor and every thing showed fine, but what could be causing my laptops screen to be so dim i cant see anything. Although i can see with it a little with the light in my bedroom shining on it.