One or two but first a quick question, where are you plugging your USB hard drives into?
USB drives need to go into the WODE unit on the side and not the Wii unit. I am sure you have not done that but lets get that little error out of the way for now shall we.
What we know is that your WODE installation is correct, simply because you are able to rip to SD card and launch games via SD card. That is good.
Could you check to see if the USB connector on the WODE base unit is correctly lined up. To test the USB connector take the LCD part out of the WODE base and connect directly to the PCB and test if that works.
Normally when I see WD hard drives I would just write the fault down to that horrid firmware found on the WD drives. But you used a SD card that was working and an adaptor that resulted in nothing being seen.
Things to do.
Flash your WODE to the latest update.
Try to connect the USB drive again.
When you post back here please include all the details from the info pane of the LCD.