re-download it and un-instill MS-Messager then re-instill it back in, after sign in with name and password. is your best thing to do.
all so go to windows update site or enable auto-update.
best have a anti-virus program that will cover MS-Messager too. there been viruses that leech into it.
Avast.com home version is free and cover a lot of areas, even going to a site were a virus maybe in the site avast will block it.
www.avast.com adware & spyware free
you have to sign-up like every 15-16mo to get a free key-code in the e-mail to unlock it.
if you do get avast and instill it let it do a bootscan same as doing it in safemod but better. you know how it look when you do a scandisk will Avast do it the same way