I'm sorry for your troubles!
Try to uninstall Boxcryptor and download the latest version from https://www.boxcryptor.com/en/download
If this doesn't work, please contact firstname.lastname@example.org referring to this thread and send them a debug log of your installation.
To start the setup in debug mode, open the run command of windows (windows button + R) and type in the path to the Boxcryptor Setup. Add the parameter "/log Log.txt" (e.g. "C:\Users\Malexandrou\Desktop\Boxcryptor_v2.0.409.325_Setup.msi" /log Log.txt)