Go here: Wii Drive Chip Database to see if you're wii has a D3-2 Drive. Also make sure you've done evrything right. USB Roms can usually be played with loaders such as CFG Loader, USB Loader GX, uLoader, etc. Be warned: these loaders ONLY load wii games.
I prefered the site: Ade's Softmodding Wii blog when I started to hack my wii.