Means that it can't find a system disk to boot from. Either the HD is dead, something is wrong on the motherboard, or the system installation is broken. Try booting from a system disc (insert a disc and hold C on the keyboard, then start the computer. Release when it starts booting) and get back to us about what happens.
Also, please update us with the model of the eMac (CPU, RAM, HD...), OS version installed and if you have done something odd recently.