How to repare Arduino Yun?

Dear Sir,
I had arduino (arduino.cc) A000008. The IDE can detect the board and port(/dev/ttyACM1’.) , but I cannot upload sketch. sometime the serial port will gone, some time report:
Arduino: 1.6.9 Hourly Build 2016/03/31 03:25 (Linux), Board: “Arduino Yún”

Sketch uses 4,536 bytes (15%) of program storage space. Maximum is 28,672 bytes.
Global variables use 148 bytes (5%) of dynamic memory, leaving 2,412 bytes for local variables. Maximum is 2,560 bytes.
Couldn’t find a Board on the selected port. Check that you have the correct port selected. If it is correct, try pressing the board’s reset button after initiating the upload.
processing.app.SerialException: Error opening serial port ‘/dev/ttyACM1’.
at processing.app.Serial.(Serial.java:125)
at processing.app.Serial.(Serial.java:66)
at processing.app.SerialMonitor$3.(SerialMonitor.java:93)
at processing.app.SerialMonitor.open(SerialMonitor.java:93)
at processing.app.AbstractMonitor.resume(AbstractMonitor.java:110)
at processing.app.Editor.resumeOrCloseSerialMonitor(Editor.java:2430)
at processing.app.Editor.access$2900(Editor.java:89)
at processing.app.Editor$DefaultExportHandler.run(Editor.java:2408)
at java.lang.Thread.run(Thread.java:745)
Caused by: jssc.SerialPortException: Port name - /dev/ttyACM1; Method name - openPort(); Exception type - Port not found.
at jssc.SerialPort.openPort(SerialPort.java:167)
at processing.app.Serial.(Serial.java:114)
… 8 more
Error opening serial port ‘/dev/ttyACM1’.

This report would have more information with
“Show verbose output during compilation”
option enabled in File → Preferences.

TX/RX/Ethernet/Power LED on. If reset yun , usb will on and off, ping 13 blink and off, if rest 32u4 TX/RX/Pin13 blink.
Wifi reset , no led will blink.

It looks like I had lose any way to talk to the board. cannot load termial, so no way to flush bootload base on the recommended. any suggestion or location where can help to re-flush this device?
Thanks
John