Guys, i’m sorry, i found out what was the problem and it was on my end . Turns out i accidentally downloaded Cubase 10.5 and not realizing it was a new product requiring a new license . I downloaded Cubase 10 and the license was working.
Anyway , as far as i understood, if you’re reinstalling windows and have usb dongle license, no reactivation process is needed , the license stays on the usb dongle as it was and the new installation of Cubase should recognize it.
If you have a software license (not a usb one) , you need to do the reactivation process and should receive a new key.
Anyway, thanks for your help!