I am facing the wifi network connection problem, which was previously working absolutely fine. I have checked /etc/network/interfaces file

auto wlan0  
iface wlan0 inet dhcp  
wireless-mode managed
wireless-essid my_network_name

I have also tried the following command on terminal but were no use

sudo ifup wlan0
fail to bring up wlan0

sudo ifdown wlan0
ifdown: interface wlan0 not configured

output of

      $ sudo lspci |grep -i network

has produce the below results

       06:00.0 Ethernet controller: Atheros Communications Inc. AR242x / AR542x Wireless Network Adapter (PCI-Express) (rev 01)