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Right....I've tried everything I can think of. Ran a full system scan by Norton (4 hours!), tried a second System Restore - Windows found C disk corrupted and then fixed it before it would let me do the restore - still the same result; I can receive emails but can't reply to them or send new ones via Windows Live mail. ('A problem occurred while trying to open this. Windows Live mail has stopped working.') Son in USA said they had a similar problem but couldn't send or receive; fixed apparently by opening IE, turning off 'working online' then on again. Tried that, same result. Fortunately it's OK via Yahoo, but it's really annoying me now.
Any further suggestions, please, or do I have to learn to live with BT Yahoo?
And thanks for your patience.