I am having the same problem you are having. All homebrew works fine, but none of the official channels work.
I even tried formatting my nand with Nand formatter which put it to 4.1 then i ran modmii and updated to 4.2 choosing to install everything, still didn't work.
I am currently trying to get SNEEK to run and gonna see what happens when i run stuff from it. Ill update when i get results
EDIT 1: Also note that my dvd drive doesn't work either, unlike yours however mine wont even take a dvd inside
EDIT 2: i tried a sneek installation using modmii and got the same results, plus whenever i tried to setup my internet connection i got an error
QUOTE said:
"Error Code: 110213 There is a problem with the WiiConnect24 service. Please try again later."
Sometimes (on the real nand) i can get channels working by repeatedly trying to open them, about once every 10 times or so and it would start. It seems random timing or whats connected doesn't effect it.