Maybe your XP Keycode has not been recognised. Like you a bit lost with this one. Maybe someone can give you the free Telephone number for Microsoft and see if they can sort it out for you. I take it that you have registered the keycode again.Was it accepted.
Always system restore but you probably do not have many restore dates.I suppose that you have tried running your security programs Malwarebytes comes recommended[free version]maybe worth giving it a try. 13 Updates coming for next Tuesday so maybe it will be Ok by then.