@sangphung
If your device has no access to Mass Storage Mode to be seen by the PC because the USB socket is damaged or it's connections to the board are faulty, then you won't be able to use preboot either. However, if your device is 'bricked' and therefore can't be seen in mass storage you will need to load cure firmware to it [Only registered and activated users can see links. ].

To gain preboot, have the nuvi completely off (not in standby) hold the upper left-hnd corner of the screen and plug in to USB to power it on. [Only registered and activated users can see links. ].

Give more information if you need further assistance.