I need to open a prior year return but am unable to open turbotax. The software asks for "activation 16-digit code" that came with the software, but I don't have it.

First a word of advice ... going forward ALWAYS save a PDF of the filed return so you have access to the return even if you no longer have the program installed.  

To find your license code:

 https://ttlc.intuit.com/community/tax-topics/help/i-can-t-find-my-license-code/01/852973

https://ttlc.intuit.com/community/tax-topics/help/my-code-doesn-t-work/01/871966

Thanks for the tip... I'd already concluded the necessity after my experience today.

I don't have any of the boxes the CDs came, so I can't activate TT.  Is there some other way or link I can access to open?  (I'd previously thought that simply saving the ".tax file" would be enough to let me view prior returns... guess not.

When  you registered the program you should have access to the liscense code ... check the links I gave you.

Contact TurboTax support and speak directly with a TurboTax support agent concerning this situation.

See this TurboTax support FAQ for a contact link and hours of operation -https://ttlc.intuit.com/questions/1899263-what-is-the-turbotax-phone-number