Been there, done that, got the t-shirt.
You can send it to Nintendo who will charge you £70, format the machine and replace the system board, which will result in a change to your system serial number, Wii Friend code and loss of all custom data on it.
If the machine is chipped you can find restore DVD images on the net, although if the machine won't even boot, I'd be surprised if they do you any good.
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