Cannot logon with current password , it tells me it's my birthdate!

If you forgot your password, you can delete it easily by using a tool in Hiren's boot CD.

There are some ways can be used for Windows 7 password reset, a password reset disk, login as another administrator account. I think you may have no one of above. If so, you can try a free tool, Ophcrack, to reveal the password. Or use your Windows 7 installation disk to reset the system to a previous point.Forgot Windows 7 Passowrd? - Windows 7 Password Reset Tool, bypass Windows 7 administrator Password Instantly.