Definitely your USB drive/port connection. 5v and GND is the easy part to troubleshoot, those are on the edges of the connector. If the current D+ and D- combination isn't working, swap them around.
postLoader is installed on your Wii, but since it reads from USB for theme stuff and everything else, that's why it's all black. Homebrew channel is upside down because it detects that IOS58 is custom(aka NoWiFi.) It still works fine, though. And if USB was working, you'd see Nintendont and other stuff that's normally in the apps folder show up.
If everything was fine on your flash drive before, then you don't have to change anything there. Either way, putting the contents of the "COPY_TO_USB" back onto the USB drive won't hurt anything.