Thank you for responding, but it's not helping.
First, I disabled my security software (Avira AntiVir) and tried to load a .co.uk site. No good.
Second, I reset the Explorer settings as you directed and tried to load a .co.uk site again. Still no good. (Security software was disabled at this time, as well.)
Also, I should add that other computers (running Windows XP and latest Explorer) on the same network CAN access .co.uk sites.
Any more ideas, please?