I'm not sure if this issue belongs here or in the Mobo Forum, but I'll start here and see what you guys think!

The Problem – Short Version
Having reinstalled the operating system after a Master Boot Record meltdown, the pc has been given a bios re-flash to the latest version, after a chipset upgrade (as recommended) and a reinstall of Windows XP SP2. In spite of this, the USB Controller and IEEE 1394 Controller Devices are not recognized. This WAS a working system.
The Cause:
In a moment of pure idiocy, I connected an external USB disk which still had its jumpers set to Master and booted the machine. It came up with a boot error (Trap 00000006 Exception Error….) and obviously hung the system. Now – with the wonderful hindsight I now have - I suspect that a recovery boot from the XP disk and running the FIXMBR command may have solved my issue, but unfortunately it is far too late for that….
The Platform :
Asus A8n sli Premium Mobo; AMD Opteron Dual Core 2.4Ghz processor ; NVidia GeForce 7900GT Graphics Card; 4Gb RAM; Win XP SP2; Lite-On DVDRW; C:\ 75Gb in RAID1; D:\ 558Gb in RAID0; Drives using Silicon Image Array Manager.
The Current Response:
I have reinstalled the RAID drivers and reset the four physical disks ( two in RAID1 for Opsys/Programs and two in RAID0 for Data) to C: and D: using Sata connections.
I have upgraded, downgraded and re-upgraded the BIOS, finally to Version 1303, the latest recommended for the motherboard. The downgrade required me to uninstall the NVidia Update application, and it does appear that only DOS based BIOS flashing works. Asus Update V7.13.04 lists Bios as Revision 1303, Chipset NZ-CK804 dated 8/10/06, which I’m pretty sure is the latest. I have confirmed that the latest Chipset Drivers - According to the directory C:\NVIDIA\nForceWin2KXP subfolder is 6.86 (Chipset drivers Version 6.65 or above are recommended for the latest BIOS)
I have confirmed that USB Legacy Support; USB Support and USB 2.0 support is enabled in Bios Configuration settings. (From Bios settings, Onboard Device Configuration; USB Configuration)
I have reinstalled Windows XP SP1, then separately upgraded to SP2. Incidentally, mouse and keyboard are connected to PS2 ports.

The Symptoms now:
On Booting, the PCI Device listing shows:-
SMBus Controller
USB 1.1 OHCI Controller
USB 2.0 EHCI Controller
Multimedia Device
And 2 x Serial Bus Controllers
all have “NA” listed against their IRQ number. Other devices use IRQs 3,5,9,11.

Windows boots fine, but the upon opening the device manager it shows error exclamation marks on:-
Standard Enhanced PCI to USB Host Controller
Standard OpenHCD USB Host Controller
OHCI Compliant IEEE 1394 Host Controller and
Texas Instruments OHCI Compliant IEEE 1394 Host Controller
And incidentally also on the Hauppauge WinTV PVR PCI II device under Sound, Video and Game Controllers.
Uninstalling and reinstalling these gives the message “A problem occurred during hardware installation. Your new hardware might not work properly.” ….Most helpful.
Updating the drivers for any of the above controllers yields the message “No better match could be found”, and manually copying the appropriate driver files to the System32 and System32\Drivers folders yields the same results.

As a peripheral issue, the DVD writer doesn’t appear to have correct drivers either, but I haven’t bothered to install vendor specific (Lite-On) drivers at this point. The CD player works fine.
I have Sisoft Sandra lite and Belarc reports on the system, which don’t enlighten me at all, but may be of use to analyse root cause or further details.
I suspected that all the above indicated a burned motherboard or motherboard component(s), but when in desperation I began an install of Vista to see if that was a viable option, I discovered that the Vista pre-install process gives the option of adding additional drivers etc from a USB device, and a Memstick connected to the USB port CAN BE READ by the Vista Install O/S. I haven’t continued with this option because I have a significant number of legacy applications that I don’t believe will run on Vista, but this is certainly a potential solution if all else fails.

My conclusion was that my issues must revolve around drivers, but given that XP SP2 standard USB controller drivers are recommended for the motherboard, and I have installed and reinstalled them into the appropriate directories, it doesn’t make sense either. Given that the forced Vista upgrade, with the extended compatibility issues, or replacing the mobo, which is less than a year old and worked fine, are my options at this stage, I’m seeking professional help!

Any ideas gratefully accepted!