DarkCorp replaces a vast majority of your IOS with custom ones. As time progresses, a lot of users end up mixing and matching (standard IOS and DarkFail IOS), which renders the Wii fairly useless for loading backups. Still, that doesn't necessarily sound as if that's the ONLY issue going on with your Wii.
I'm hoping you verified the make/model of your USB drive in terms of compatibility (not that our list is complete by any stretch) and that you properly configured it.
Simplest suggestion: do a NAND restore and follow the "Softmod ANY Wii" guide. Then verify it works via optical. Then try the USB drive. That should be a basic process of elimination thing. Alternate suggestion: follow that guide right now without the NAND restore.