I used Turbo Tax last year but did not owe taxes. I want to use again this year but it won't allow me to add my banking information, why??? I have not filed my forms yet.

Did you already e-file?  If you did NOT e-file you can go to the FILE section and change how you want to receive your refund.  If you want direct deposit you need the routing number and your own account number.

You cannot  change banking information while your return is in pending, nor can you change it after the return is accepted.