The easiest way to recover the admin password on a Windows server with a Plesk installation is accessed by a shell or terminal server and run this command.
"%plesk_bin%"\plesksrvclient.exe -get
the window wont open with the Plesk admin password.
You can also assign a new credential with:
"%plesk_bin%"\plesksrvclient.exe -set
If we add the final true also change the password of the Plesk database. Finally, if we use instead of drawing -nogui the result by the display screen in the console and send the password to the clipboard.