Just keeps asking for a prepayment or activation code

Good morning,
Clear your cookies and/or History.  Sometimes security features are set so high, that they block payment screen and Netfiling.  You may have to turn off your firewall and anti-virus programs until payment and Netfile are completed.  Log back into your account.  You should now be able to enter your payment or payment code.  
Thank you for your question.
Leeanne@TurboTax

How do I get my code

If you do not have a prepayment code you can look further down on that page and click on continue. Then you will enter your payment.