For the longest time my wifi (which is an Atheros ath5k) has been reported as hard blocked on Ubuntu.
There doesn't seem to be a pattern, but when it works, it works for a long time... then all of a sudden it stops again.
The fix seemed to be a rather strange one, but never mind, it works. Run this in the terminal:
Text Snippet:
sudo rmmod -f ath5k
sudo modprobe ath5k
I'm not saying this will definitely work for you, but for me at least it does.
Hope it helps someone out there!

Alifia commented on Oct 21st 2013