Arduino Yun serial port FAILED?

Hi,

I have two 'arduino yun' boards are facing the same issue as below:

  1. Yun can detect the serial port and run the code, but I can't print any status on terminal in OS win 7 when I run the
    'YunSerialTerminal' after boot up ?

  2. And I found that the USB led always high and the YUN RST button can't work (no response)? (Please find the attached file)

  3. I have tried to use the "AVR Dragon" (with atmel studio) to burn the bootloader "Caterina-Yun.hex" via ICSP port and make sure that the register setting as below is correct,

a. yun.bootloader.low_fuses=0xff
b. yun.bootloader.high_fuses=0xd8
c. yun.bootloader.extended_fuses=0xfb

After that I reboot again, but Yun can't back to the default factory setting.

I can't find any wifi AP name of Arduino Yun on the PC and the linux can't display on the terminal after upload the
'YunSerialTerminal' and boot up.

How can I do now? Please help ... ... Thanks