MISSING OPERATING SYSTEM

hiya, Right my sister absolutely ballsed up her brand new ACER ASPIRE ONE netbook she had for christmas the other week, and ive tried to fix it myself but there is no fixing it, it says the operating sytem is missing, which therefore leads to me not being able to restore the laptop to any earlier point in time, fix problems manually or even let me set the settings back to factory default!! i really want to avoid having a ''professional'' fixing it therefore any suggestions would helpppppp i hAve absolutely no idea now where to start fixing it, Any help would be much appreciated Thanksss!

Oh and also the laptop will not even start up it gets to a point where it sometimes lets you onto restore options but none of them work, so i believe anything im gonna have to do will be through a USB, therefore i set the USB as the first reboot option...