can't login to email

Once again I am not able to log in to my email account from my home computer.  My password gets me into my att billing page, but it will not get me into my email.   I have experienced this problem several times over the past week.  The same username and password works on my smartphone.  What's up!  I was already unhappy that I could only get to my email by logging in to att.com and going to email from there.  It is ridiculous to have to enter the same username and password three times just to get to email.