cannot change password

usually when I go to change my password, I get a screen with three boxes:
Current password
New Password
Retype New Password

but the last couple days when I have tried to reset my password for fear of it being comprimised, I get a screen asking me to login, and when I enter myu information, it says "cannot log in"

can anyone help?

I don't really understand you. You wanna elaborate? Basically, you just have to enter your current password and new password to change it.