I recently bought an arduino yun. When trying to connect to the router following the procedure in https://www.arduino.cc/en/Guide/ArduinoYun#toc14. After the Configure & Restart, the Arduino network shut down after a few moments but it wasn´t linked to my router.
After reading a bit about it in the internet, i upgraded it following https://www.arduino.cc/en/Tutorial/YunSysupgrade. As i found that the firmware version 1.5.3 was from 2014 https://github.com/arduino/openwrt-yun/blob/master/ChangeLog, and as Reflashing the OpenWrt-Yun image on the Yún would void warranty, i proceeded by http://nootrix.com/software/upgrade-arduino-yun-openwrt/. Everything occured as detailled there.
However now, when i turn on the yún, none network appear and the WLAN LED doesn't blink.