Do u have priiloader installed? If so do this:
1. Pull ur wii power plug out and wait 5 seconds.
2.Then plug it back in. Now press and hold reset button (keep pressing it).
3. While pressing the reset button, press the power button. do not let go of the reset button.
4. The wii should boot to the priiloader menu. From here u shud be able to open system menu, open homebrew channel or bootmii.
5. You can install the default theme from the homebrew channel or recover a bootmii backup if needed.
GOOD LUCK!