This happens occasionally. Never been able to figure out why or how to revert it.
It's often varying causes and effects but right now, when I am in Outlook Express on W7, if I press the ? key, I instead get a É.
I'm sure it's a keystroke combination that activates some obscure language setting such as a French kb, but I don't know how to revert it.
I've gone into Control Panel keyboard and checked to make sure that English US is the only thing listed. No joy.