I've been having this problem where my GFX fan has stopped spinning.
I don't know when it stopped; only noticed when my performance started tanking.
After some on and off changing, I noticed that my fan does in fact spin, but somehow only when the Card's drivers are disabled.
I've updated my driver to the latest (automatically first, then manually due to the fan not working) update available, to no avail.
Any thought or reason why?