Bad optical drive. Wouldn't read Wii discs anymore. Very common problem from what I hear. Nintendo refused to service it and sent it back. I own an original 2006 model, it is no longer under warranty and I paid them for repair that they offer but they said I opened the case and just for doing so they refuse to repair it. I was/am furious. I've been in IT for ~16 years and took great care in opening it to clean the lens but to add to my anger Nintendo actually returned my Wii to me in pieces with stripped screws. It's also worth noting that if you buy a full system as replacement you will need to repurchase downloaded games as they are tied to the device itself and Nintendo will not transfer them. And to add pain the newer Wiis do not play Gamecube discs at all anymore. No more Nintendo for me.
A couple of the tiny screws are difficult to place and require tweezers. Also the power and data cable are tiny and require a good deal of patience and steady hands. Nintendo stripped some screws (2nd photo center .. power driver?) one of which I actually had to drill out it was so bad. And they lost the nut for the battery door (1st photo) so I have to tape it shut now. Other than those fun surprises from Nintendo all went pretty well.
You'll need patience and hands that could play the game Operation. Other than that it is a simple matter of following the detailed instructions available on the site in PDF format. I was concerned that the drive board layout was different (see 3rd photo with old drive left and replacement drive right) but no problem .. works with 12cm (Wii) and 8cm (Gamecube) discs as advertised. Kids are very happy daddy fixed it.