Well, your Wii's Disc Laser Reader might be broken.
The options are to buy, a new Laser for your Wii, and repair it yourself.
http://www.dealextreme.com/details.dx/sku.19842
Or.
Send it in to Nintendo for repair, and hope they don't do anything to your Homebrew Channel, or anything else you have installed. Is the warranty still active?
http://www.nintendo.com/consumer/orders.jsp
Lastly, try to look at the troubleshooting Q, and A, on Wii Discs.
http://www.nintendo.com/consumer/sys...jsp#recognized