Clarification/Follow-up by MikeR on 11/09/06 10:32 am:
Many thanks for detailed suggestion - I now have a copy of my h/w config! In fact I realised I had nothing to lose & tried removing the device in Device Manager. I also tried disconnecting the cables & verifying that the drives no longer appeared in DevMan. Upon reconnecting, they re-appeared but Windows cannot find them.
'Update Driver' says the best available driver is installed.

I now recall that during my abortive attempts to instal NERO Essentials (sorry, Mero was a typo) I cleared out some 'redundant' files with WinOptimiser & suspect I have deleted something critical. It won't be in the recycle bin .....

I've updated my backups on an external drive with a view to a rebuild, but should I be able to repair the system, even tho I have no idea what's missing?

Clarification/Follow-up by Pride_of_Alderaban on 11/10/06 2:47 am:
Hi
When we are playing around...

Familiraze Yourself with Verifier.exe

I suppose You don't have a clue what it is (most people don't)

Just RUN verifier.exe

Set it to use Special Pool

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It's kindly delivered with every XP OS by the nice guys at Microsoft without telling anyone....

The handiest way is to search for Verifier.exe
then create a shortcut to it on Your desktop

It will slow down performance so You should only use it when having trouble...

To Deactivate it just run it once again before rebooting (Setting the options You want to use)
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Back to topic
If You have backups I think the easiest way is to do the following

1.Make a WinXP repair of OS (Reinstalling with the r option, Since I never tried it, just ask ScottGem... He will give You full details in how to...

2.If that doesn't help...
Then Your "lucky", Now is the time to reconfigure Your hard-drive and eventally boost the performance of Your PC slightly by running the SwapFile/PageFile on a separate partition,
or in a case that You have two HD's, then You should run the SwapFile/PageFile on that HD on a dedicated partition
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This part taken from The Langalist std Edition:
Hi Fred, Just a quick question about the Windows XP paging file
which you wrote about recently. In Windows 9X a useful trick with
swap file was to make the minimum and maximum equal so that Windows
did not waste time enlarging and shrinking it. This was said to
give a small improvement in efficiency. Is there any merit in doing
the same thing with the XP paging file? Regards, Peter

In a word, yes. The reason is that the "Initial size" of your paging file
(formerly known as the "swap file") is really the "permanent" part of your
paging file. The difference between the "Initial size" and "Maximum size" is
really the potential size of a temporary paging file added to the permanent
one. That temporary file will be sized and created as needed and on the fly,
potentially grabbing chunks of far-flung disk space wherever it can. In other
words, it may be defragmented and thus degrade the performance of virtual
memory.

By making "Initial size" and "Maximum size" equal to each other, you're
really just telling Windows that you want nothing to do with temporary paging
files, and that you want only one sufficiently-large permanent one. By
defragmenting your disk before creating this permanent paging file, you'll
make sure that the permanent file isn't fragmented, either.

Here's how to get to the Virtual Memory dialog box, which governs your paging
file: Right click on My Computer, choose Properties, then the Advanced tab.
Click on the Settings button in the Performance box. Click on the Advanced
tab, then the Change button.

The first step is to get rid of your paging file by clicking on the "No
paging file" radio button. Click on the three OK buttons, defragment your
disk, then reboot.

Defrag to open up contiguous hard disk space, and then go back to the Virtual
Memory dialog box and set the "Initial size" and "Maximum size" to the same
number. You can use the "recommended" size shown in the dialog; in XP, the
recommended size is usually fine. But if you prefer to pick a different size,
a good rule of thumb for most users is to create a paging file that's 1.5-2
times the size of your physical RAM. Then, click OK three times and you're
done!
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The Above refers to using the same partition as the OS itself.
By moving the SwapFile/PageFile to a separate
Dedicated Partition is even better
Also by making the dedicated partition a FAT instead of NTFS will give a slight performance boost since FAT is somewhat faster than NTFS

Enjoy!!!

Janne alias Pride...