Just as an update:
I ended up opening the card (it is surrounded by one of those plastic all-encasing sleeves) and a part (what I assume to be the sensor) dropped straight out. It was a flat little circular piece, a but like a small coin or battery. I located where it had come from (right next...
Thanks for that. Whether or not I have have access to the fan header, I'm probably not skilled enough to fiddle with it, so I'll call it "dead".
It seems an awful waste for a whole card to now be useless because of such a tiny failure. I might try get on to gigagbyte and whinge in their ear a...
The fan on this card suddenly ramped up to 100%--noisy as anything!
After multiple restarts the fan remained at 100%. Looking in catalyst, there is no sensor information at all, except the temperature listed as -128 degrees c.
I am guessing my sensors have died and the card is maxing out the...