I had that issue once, and it went away after I did the "+ -" at the health screen. After that it never happened again. I don't think Det1re's Mailbox fix is up to date, it does not seem to work for anyone. But I don't think it is your message board, when that goes bad you should have a black screen after the health screen but it would work with + -. I don't know what it is.
You can try-
-Leaving it alone
-Disabling priiloader hacks
-Reinstalling ios60-v6174 and SM 4.1u
-Formatting the system from the wii settings.