Good day! I updated the firmware of my RB750 to the latest version available on the official website, everything was fine until I turned it off. When I turned it back on it constantly restarted and made a beep (sound).
I tried to reset it with the button for that purpose and also using the internal reset. But there is no way

This is a quite well known problem of current stable version (6.49 and possibly 6.49.1). The only way to revive such device is to use netinstall. Beware that netinstall is a very fragile process and everything has to be done perfectly or else it will fail one way or another. So if it seems that your device can't be netinstalled ... it's actually that you're doing something wrong.