When it doesn't work, you switch it on and you get a plain black screen with a few odd white pixels in the middle (like they might have been bits of words)
Nintendo states on their website that if the error is a black screen when you turn it on then it needs returning to them so we'd be grateful if you could do this for us.
They say
QUOTE
If you have verified the connection is correct, and are still receiving a blank white or blank dark screen when powering on your Wii console, then the problem is likely with the system and it will need to be repaired. Please click here for repair options.