Instructions
Turn on your Nintendo Wii and wait until the "Health Warnings" screen appears.
Hold the plus and minus buttons simultaneously, wait a few seconds, then push the A button.
The Nintendo Wii will notify you that you are in "Maintenance Mode." Try clicking on the Wii Message Board and you will see it is disabled.
Once you've explored the relatively similar to normal "Maintenance Mode," reset the Wii to make sure there is no loss of data.