Instructions
Turn off your Wii. Turn it back on. Sometimes this will fix your issue. Check your connections. Make sure your Wii plugs firmly into the "Input" slot on your television.
Find your product warranty. Figure out whether or not you still possess warranty coverage. This will save you money and get you a free repair as long as you took no illegal action with your Wii.
Call 1-800-255-3700 as of July 2011 to talk to a Nintendo representative. Set up a repair. The representative will instruct you on the steps you need to take to get your Wii repaired.