This game console ended up in repair after trying to change the main menu theme. If BootMii isn't set as boot2, you shouldn't do such manipulations, it can lead to the System Menu ceasing to run, as it happened in the case of this console. There are no backups and no way to start anything. All we have is a black screen.
So, take the console apart, find and unsolder the nand flash, the Wii has 512 mb of it in a tsop-48 package.
Dump, in our case using teensy 2.0+ and a little modified nandway.py for ps3, replace original boot2 with patched bootmii using wii flash toolz. But there is one condition here - the console must support this feature, which means it must have been produced before about the fourth quarter of 2008. We are lucky)
Fill the dump back and add to the sd-card the files needed for bootmii and start the device with reset button pressed.
Choose "make backup", we get a dump with the keys. Open ohneswanzenegger, press "create new" and choose ours as a base for the new one. Then format and install the necessary packages (system menu and others necessary for normal operation), you can use NUS Downloader for this.
Fill in setting.txt (location, model, serial number of the device) and get a working dump of the device on the sd-card. Go back into bootmii and choose restore. After that everything should work.