wifi failled connection with yun and after upgrading openwrt
Find out if the Linux system is running. Maybe you mistyped your WiFi password.
Try the Following: 


connect via Ethernet check your router to see if the Yun request an IP via DHCP
If unsuccessful connect via USB and install this sketch to see if you get a command prompt maybe your network settings are messed up 


Still no success?


Press the WiFi reset button for at least 30 seconds to do a reset to
factory defaults.