After switching back to bash can't access root

After switching back to bash can't access root

I'm new to Linux and using Debian 7. I was using bash, but tried out zsh
by using chsh. Initially probably entered a bad shell name but eventually
switched to zsh successfully.
Now I switched back to bash but can't access root
When I hit su and the password it returns "Cannot execute zsh: No such
file or diretory", while apparently I'm using bash.
Additionally, when I changed back to zsh it still said the same, "can't
execute zsh ..."
Can someone help please?
Thanks!
violeaf