It is just a note that has helped me to resolve problem with Wi-Fi broken connection after system upgrade in Ubuntu 14.04 on a laptop DELL Inspiron 3537.
What: after system update Wi-Fi connecction does not work despite hardware Wi-Fi module is switched on (Wi-Fi connection LED is ON on the laptop) – transmission power is OFF.
$ iwconfig eth0 no wireless extensions. lo no wireless extensions. wlan0 IEEE 802.11bgn ESSID:&amp;quot;FlatNetwork_2.4GHz&amp;quot; Mode:Managed Frequency:2.462 GHz Access Point: 10:FE:ED:FF:D2:AD Tx-Power=off ... ... ...
Transmission power is off (Tx-Power=off) as you can see it from the example above.
Solution: solution is pretty simple in my case, I have not dug why it may happen after system update, but it is enough (at least for me and for the considered problem) to down wlan0 network interface, then up it and reboot the system:
$ sudo ifdown -a $ sudo ifup -a $ sudo reboot 0