If you have a NAND back-up, then it can always be fixed (unless it's the hardware). You can do the following:
- Turn on the wii and watch how many times the disc drive light flashes. If it flashes twice quickly, then you can use bootmii to fix your wii.
- If you don't have bootmii/boot2, you can try holding reset when you turn on the wii. If you can launch priiloader, then you can use it to fix the brick.
- If that doesn't work, you can try savemiifrii.
- If savemiifrii doesn't work, a hardware NAND flasher can be used to flash the NAND back-up to the NAND. You can do this yourself (if you have a NAND flasher), or have it done by a wiihacks member (for a price of course).