Could be a D3-2 drive (unable to play backups)
Plug your Wii serial number into this Wii Drive Chip Database
If it is a D3-2 drive then you have a few options....
1) Play only retail purchased game discs (yeah right!)
2) Play your backups using USB Loaders and devices (ftw)
3) Buy an older drive PCB off ebay and swap with the D3-2 you have (also ftw)