If you tried using several different microUSB cables, different REAR USB ports directly [no hub] and even tried with another PC without being able to hold either preboot or mass storage mode, then it's probably got some hardware damage or failure, either the USB socket itself or the socket's connection to the board. I can certainly help you to load new firmware using SD txt commands. However, you did say this in Post #5:
Quote Originally Posted by sangphung View Post
i use kaspersky internet security on pc, when i connected nuvi whit pc, kaspersky deleted some file on my nuvi, and then i connect nuvi into pc again, it not recoginize my nuvi
  • So you had PC recognition before that. It might be co-incidental that it's got a damaged USB socket connection about then (but I really don't believe in "co-incidences" much).
  • If the above circumstance with Kaspersky is the cause why do you think re-loading firmware will fix it?
  • What fw version is it running now?
  • Have you hard reset it and cleared NV?


Please clarify those items before we look at using SD txt commands.