Do you have BootMii as boot2? or Priiloader? If you have Priiloader, hold Reset when powering on the Wii and the menu should pop up. Also, do you have a NAND backup from BootMii? If so you can send your Wii to someone to fix it if you don't have BootMii or Priiloader. If you don't have any of these things then you cannot fix it.
Priiloader won't work without a working System Menu IOS, the only (software) thing that could have fixed this would have been BootMii/boot2. Seeing as you do have a NAND dump (presumably taken with BootMii/IOS?), you could find someone with a hardware NAND reprogrammer to reflash your Wii's NAND (involves dismantling the Wii and connecting a chip from inside to a computer). There is a guy who goes by the name DeadlyFoez in the Wii "scene" who can fix Wii's in this manor.