Thanks danleff for the suggestion.
Sadly the makers weren't much help!
However, I did have a look at the Tyan page you suggested and there I read that I need to disconnect from the mains before flushing the BIOS (whcih I hadn't done!).On reflection, this is bleedin' obvious but I didn't realise it !
I have done so - disconnecting from the mains first - and all has worked fine, so many thanks for your excellent help and advice!
Cheers and thanks again
Chris P