What Nintendo does when they're to repair a console, but instead send it back due to tampering is a mystery... I sent mine in since it played no games, and it came back playing everything but dual-layer discs, even though they didn't repair it due to discovering tampering.
I've never seen anyone's Wii simply not respond to a disc. I don't have any tips unfortunately, only a recommendation. If you can find one, send it in for repairs to a non-official repairing service. Certain gaming stores offer said repairs, some of 'em with guarantees.