If the system doesn't accept the password or the answer, open the browser, press Ctrl + Shift + Delete key combination, clear all cache, cookies or temporary Internet files and try again. If it still doesn't work, verify if you entered the correct password and make sure you're using the correct uppercase and lowercase letters. For further solutions, I suggest you check the official Support page. Also, you can use the 00 1 800-318-0612 phone number to contact Yahoo Customer service.