Instructions
Press the "Eject" button. There are three ways of turning your Xbox 360 on: pressing the "Eject" button, pressing the "Power" button and using the Xbox 360 controller. If your console turns on with the "Eject" button but not the "Power" button, the faceplate is not attached properly.
Check the power supply. Ensure that it is plugged into both the Xbox 360 console and an outlet. If it is, disconnect and reconnect the power supply.
Plug the power supply itself into a wall outlet if you normally use an extension cord. Extension cords can become damaged and not work correctly.
Check the power supply light. If it is red, the console has overheated; you need to unplugged it and let it cool down for an hour. If there is no light or the light is orange or green and your Xbox 360 will not turn on, either the Xbox 360 or power supply is malfunctioning. Contact Microsoft to get either one replaced.