Instructions
Check the Wii connection cables to make sure that the end connected to the Wii is plugged in all the way.
Unplug the yellow, white and red AV cables from your TV and then reconnect them, making sure they are plugged into the correct inputs.
Hold down the "Power" button on your Wii for at least 10 seconds and until the power light turns red.
Press the "Power" button again and make sure your TV screen is turned on. Make sure the correct input is selected on your TV that your Wii is connected to, such as "Video 1" or "Input 1."
Unplug the AC adapter from your Wii and the reconnect it if the Wii continues to only boot to a black screen. If the problem continues, you may need to contact Nintendo Support.