Hello speed420,
If you signed up with a live account or email address. You may want to use the live sign in page that is located underneath the sign in box at adcenter.microsoft.com.
Here is the link:
https://login.live.com/login.srf?wa=wsignin1.0&rpsnv=11&ct=1265120425&rver=6.0.5276.0&wp=MBI_SSL&wreply=https:%2F%2Fadcenter.microsoft.com%2Fdefault.aspx&lc=1033&id=264263
Thank you,
Microsoft Advertising Support