Acer Netbook Model ZG5

Hello,
My Step-Daughter has some how deleted the system! Well, I don't know what she's done or how she's done it!
She has an Acer Netbook ZG5 and I press the power button and nothing even comes up on the screen. When it's got the charger in, the power light comes on and you can hear the power is on but the screen is black! Please help. She won't do this again I'm sure because she's missing it so much. She's 10! Please help me somebody!!!

Thanks,
Kaz.x