DM,
I've now tried running the PC with both optical drives disconnected, just in case a firmware problem with one or both of them might be the cause of my problems with this US3L, but no joy, I'm afraid. I also tried the drive connections in the other Intel SATA ports, to eliminate the probability of a 'fit' problem. Again, no change.
I then used my imaging software (run from a floppy disk) to restore the PC to the earliest image I made. This image was of Windows XP + Service Pack 3 for WinXP + motherboard drivers. Unfortunately, Windows XP has a habit of requiring Activation in those very early stages and I didn't configure my setup for online operation until several stages later, so when I now came up against this in the Restore, Windows would only boot as far as the Welcome To Windows screen. However, I could already see from the PC's frontpanel HDD Activity LED that operation had entered the unstable condition to which I've already and constantly aluded. There was nothing more I could do, or needed to do really, so I restored back to my current image.
Other than a PCIe graphics card (high-calibre, non-games), I use no other plug-in cards inside the PC, so I think you'll agree that this, together with all the other testing I've done, is conclusive proof that the problem must be caused by either:
a) a faulty BIOS FH (faulty data);
or
b) a faulty Intel INF driver;
or
c) a faulty motherboard (possibly, a damaged BIOS chip).
