I was trying to find the best thread to post this info. I just had a Wii that would not sync any controllers....it just stopped working. This was at my buddy's house and he live pretty far away. None of the normal stuff I told him to try worked.
Anyway I visit him (it hasn't been working for at least a month) and see the same thing. I even used priiloader and a game controller to redo the soft mod and still nothing.
Anyway, I had to unplug the thing completely for around 30 minutes or so. After that it worked perfectly. Tried uplugging it before obviouslly but it didn't fix it. Had to leave it unplugged for a good amount of time. My understanding is if the Bluetooth is bad the console won't boot.....so the Wii is just getting confused somehow. I am thinking this may be related to softmodding perhaps???
Doesn't seem likely to be the mod, all the Wii's I've done have never had any problems aside when using a new TR+ remote in which case doing as Maui said in this thread worked for me. It's more likely related to the WiiMote than the mod (I'm guessing).
The only other thing it might have been was third party controllers screwing up the wii. He was using knockoffs when the problem started but He bought brand new ones ( wii motion plus wii u branded ones)and they didnt work either and when I got there I tried my original launch era official controllers (they work fine i use them all the time)and they didnt work either.