Advice I got from Wandy below:
'If you've reinstalled Windows and you've used various drivers AND have had
the card pass tests on three separate occasions, it's your motherboard --
or a significant incompatibility with it.
The only advice that makes sense would be to go buy yourself a replacement
Abit AN8 Fatal1ty: if you were to convert time and worry into pounds and
pence, I dare say it would be more than the £135 it would cost you.'
I am going to run Knoppix disc utility tomorrow night and see what it picks up. Then it looks like I am going to have to take the whole PC apart (oh the joy) and then send the board to Scan for testing and then await a reply and maybe then get a replacement and then rebuild.
If knoppix fails to pick up any irregularities I may try loading SP2 for XP just in case...