MS Outlook problems

I've been using Outlook for email for years and suddenly every time I open the program and hit Send/Receive a box appears that asks for my user name and password.  I enter the correct information, but the box keeps appearing and will not allow me to receive or send email.  I have to correct the situation by going to the Cox web site, logging on, and change my password.  In fact, I don't really change the password, I simply indicate that I'm changing it but keep the same password.  I'm then able to again receive and send email using Outlook.  Once I close the Outlook program and reopen it the same thing ocurrs again.