Did you already install it on another computer? Do you have the 16 digit License Code? There should be a card in the CD case that says how to download it and you will need the 14 or 16 digit code from it to enter.
How to install TurboTax CD/Download software with license code
https://ttlc.intuit.com/community/tax-topics/help/activating-turbotax-cd-download-software/00/852971
