Instructions
Unplug every cord that connects to the Wii, including the power cord, the TV screen cord and the Ethernet cable, if you use a wired connection with the console.
Unplug the AC adapter from the wall.
Let everything sit unplugged for at least two minutes. This will reset the Wii and the adapter.
Plug everything back together, making sure to press the plugs firmly into their proper sockets. Also make sure the wall outlet is working properly.
Check every cord and accessory for damage, particularly frayed wiring, if the Wii still doesn't turn on. Make sure the power adapter says "Wii" and "RVL-002." Remove any accessories that are not specifically designed for the Wii, including memory cards and controllers. Elevate the Wii to give it ventilation, and check for dust or debris that may clog the ventilator.