Hi Diane,
Welcome to the forums. I see that even though you registered a while back, this is your first post. It's good to have you on board!
To continue on from what Dan said...
The "Key" setting is located as shown below (if you have BIAB 2015). If you have an earlier version of BIAB, it will be somewhere near the "Tempo" setting.
This can be set by clicking on it. As Dan has already mentioned, after doing that, you'll get two options.
If the key is already set to "C", it might be that somehow the program has engaged one of the instrumental transpose options. Again on version 2015, this can be accessed by clicking "Chord Display" (#1 below).
Double-check that it's set to "(default) Concert Key" (#2 below).
Let us know how you go.
All the best,
Noel