We need to get a new driver to try to fix the issue you are having:
Install the dependencies required to compile the driver:
sudo apt-get install --reinstall linux-headers-generic linux-headers-$(uname -r) build-essential dkms
No internet:
On another computer go here Select Trusty in the drop-down box. Search for linux-headers-generic, build-essential and dkms. Be sure to locate their dependencies and the dependencies of the dependencies.
Download the correct version, either 32- or 64-bit. Once you've download about seventeen packages on another computer, transfer them with a USB stick to the desktop of the computer with Ubuntu on it. Then do:
cd ~/Desktop
sudo dpkg -i *.deb
Then:
Go here and download the driver 3.15-rc1-1 to your computer then place the file on your desktop and right click and extract here.
Then compile the driver using the directions below.
cd ~/Desktop/backports-3.15-rc1-1
make defconfig-ath9k
make
sudo make install
sudo modprobe -rv ath9k
sudo modprobe -v ath9k
When you have an upgrade to the kernel you will need to do:
cd ~/Desktop/backports-3.15-rc1-1
make clean
make defconfig-ath9k
make
sudo make install
sudo modprobe -rv ath9k
sudo modprobe -v ath9k