I signed up with msn. For the first hour i was able to log in. But then when i tried to log in i got You can start using your Microsoft adCenter account as soon as you activate it. To do this, open the confirmation e-mail that is being sent to you in the e-mail address you provided during signup. (If you don't see it there, please check your Junk Mail folder.) But there is no any mail with confirmation link. Just welcome e-mail and setup fee charge report. Do you also get this message after sign up?
You just contact MSN Adcenter Support team and enquire them about the issue what you are having. They will guide you.
I have had that before and it was because they thought there was a security issue. You must contact support.