Hi Anne-sophieb74938933,
Kindly check and confirm the system requirements for Dreamweaver CC 2015 are met: System requirements for Dreamweaver
After this please check in your installed Programs/Applications you should have Adobe Creative Cloud installed, launch it and sign in with your Adobe ID( email address ).
Until and unless the Creative Cloud Desktop app is running fine, the products will not install.
If you don't see Adobe Creative Cloud listed under your installed Programs/Applications then please download it using the following link : Download Adobe Creative Cloud apps | Free Adobe Creative Cloud trial
Once installed Sign in with your Adobe ID( email address ), then click on APPS tab and click on TRY for Dreamweaver to install the trial.
Also see, Download and install Adobe Creative Cloud apps
Let us know if this helps.