Thanks for your reply.
I plugged the USB HDD in to get you the BSOD error info... and no BSOD. I rebooted with the USB HDD connected - no BSOD.
The last thing I remember running was a "MS winxp malicious sw removal tool". I ran it over night, but it had crashed and gave me no report. Maybe it fixed something, or maybe posting here fixed it!
Thank you very much for your time. The problem is fixed, but if it happens again, I'm not sure how to fix it! ;-(
This is my first post. Do I need to do anything to close it?