have you tried signing in from a different computer/device?
iPhone auto capitalize the first letter, Good idea is to always use a number as the first digit, like a former address you had.
Also could be that you have a bad key on the keyboard, what happens when you open notepad and type the password?
it is also possible, though unlikely that key has been mapped to other character.
No, that’s not exactly it.
The address yahoo wants to send the verification code to is correct but their email never shows up in my inbox. I’ve called my internet provider but they’re clueless.