Following quote comes from another thread, dealing with a nüvi 750:

Quote Originally Posted by Neil View Post
<...> Did you put the nuvi properly into pre-boot? It's a little different to others. Firstly have updater.exe open on your desktop with the *.rgn file already loaded and a dot in the 'USB Device' radio button. With unit OFF hold the upper RIGHT corner of screen, slide power button to left then quickly to the right to lock and as soon as the Garmin logo appears immediately plug in the mini-usb to the unit. When your unit's details appear in the USB Window of updater.exe, quickly press the 'OK' button.
A friend of mine has a bricked nüvi 765. Would the procedure to get it into pre-boot mode be the same as described above for the nüvi 750?