It may just be a passing issue with Hotmail / Windows Live. The issue might go away after a while.
It may also be that there has been some suspicious activity with your account. I.e. someone is attempting to login to your account. It's probably worthwhile reviewing the security on your account.
While I'm here, if you are using the Live messenger, you might want to consider using Pidgin
instead. You can just configure it to log into your live account. I switched years ago when Live messenger got rather ad heavy.