My emachines computer is not starting whats wrong?

hi i have an emachines desktop computer that isnt starting up. so heres what happend i shut it down and i had to unplug it, it was unplugged for about an hour, when i plugged it back in i pressed the power on and absolutly nothing happend. ive tried a few things --- its not the power box, its not the power on, its not the wall socket, ive tried taking out the ram and startin it up and that didnt work, so im guessing its the motherboard but theres a green light on the motherboard thats lit up when the power supply is connected.