Ensure the USB drive is plugged into Port 0 (the bottom port when the Wii is standing vertically). Verify the drive is formatted to FAT32.
You can easily convert bulky ISO or newer RVZ files into the WBFS format. Tools like Wii Backup Manager allow you to simply "Transfer" a file and select WBFS as the output. roms wii wbfs
Offers a highly customizable, modern user interface. Ensure the USB drive is plugged into Port