Just to add to Gord's response.
Excel has a few XLStart folders. And if you have a *.xlb file in each of those
files, then you could confuse excel. It'll open up each file (I'm not sure
about the order, but it's not what you want!).
And you could be saving your changes to the right folder, but when you reopen
excel, those changes get overlaid with an older *.xlb file (from a different
folder).
I'd close excel and look for all *.xlb in all my folders (look for hidden files
in hidden folders, too).
Then I'd delete/rename all of them.
Start excel and make a change to any toolbar.
Close excel and reopen.
If it worked, then make your real changes.
Later, search for that *.xlb and back it up to a nice location. You'll want to
put it back into the correct location after you make a change you didn't mean to
make (it happens!).