I firstly installed a Photoshop trial on a D:\ partition...after 3 days i unistalled it and deleted this partition (so i don't see d:\ on "computer")
now i'm trying reinstalling it but it still tries to install it on an inexistent partition
This is very strange, As per your steps, the path that should come on installation should be of default location which is Root drive.
i.e “Root Drive”\Program Files\Adobe. Not the custom path as you reported.
Please ensure your uninstallation was clean, After that kindly restat your system and verify this issue again.
If issue persists please provide us with the details of the system you are using and the exact steps which resulted in this issue.