Instructions
Check the composite cable connection made between your Nintendo Wii and your TV, if applicable. This is the standard audio/video connection, and this composite cable ships with the Wii. Look at each end of the cable to discover that each end possesses one red, one yellow and one white plug. Find the composite ports on the back of the Wii and the back of your TV and ensure that the plugs and ports are matched up via color. A yellow plug cannot be connected into a white port, for example.
Check the component cable connection between your TV and the Wii if you have opted to use this kind of audio/video cable instead of the composite cable. Component cables have one red, one blue and one green plug on each of their ends. There are red, blue and green component ports on the rear of the Wii and the TV. Ensure that the plugs and ports are matched up properly. This should fix the black screen problem without the aid of any modchips.
Observe the color of the Wii's power indicator light if the screen remains black. If it is green or orange, hold down the power button for 10 seconds and allow the system to shut down.
Unplug the power supply of the Wii if holding the power button down for 10 seconds does not work. This will effectively shut off the console.
Wait for the Wii to reboot after pressing the "on" button on the machine. The system should be unbricked, and audio and video output for the Wii should be restored to your TV.