I have DFI Tech support responding slowly, I think they ration it to one reply a day, but they are not being particularly helpful yet..
So far I swapped out my 790FX board for an old DFI nForce 4 board, and hammered the disks for a few hours yesterday without so much as a bleat from them.
So bit the bullet and swapped boards again, and have the 790FX back in and went for a format and clean install of XP.
I have to question the quality of the AMD/ATI drivers, once you find them which in itself is a major feat now.
I had to use google to get some idea as to what the driver file would be from ATI for the Sounthbridge and SMBus, before I could then start a search of the ATI site to find the download....since AMD took over ATI has gone to pot.
Anyways, I will now soak test again and see what occurs..