Okie I think this might help.
When I bought my wii fit,
I had no problem with the balancing board until I start trying the game,
The game doesn't seem to start.
I brought my balancing board back to the store and ask for an exchange and somehow it works.
So I bring the board home.
and I tried it again without connecting my nunchuck to the wii remote.
My board works.
I figure out that some game may not start because the nunchunk is connected to the wii.
I hope this help.