1. Disconnect the Micro USB cable (if connected) from your Nexus 7 then press and hold the power button for 15 seconds.
2. If your device doesn't start up, charge your Nexus 7 battery:
a. Connect the bundled AC adapter to your Nexus 7 then charge your device for at least an hour.
b. Press the power button again. If your Nexus 7 still won't start up, please contact ASUS customer support.
Note: Ensure that you use only the bundled Micro USB cable and AC adapter to charge your device.