Viewing my att webmail with Seamonkey

I have been getting my webmail from att.net for a long time and about 2 weeks ago, I started to have this problem:
I sign in with a password and am directed to a page which shows all the emails in my "Inbox ". When I click on one of the emails it is supposed to open and show me the contents. Instead, I get a blank white page. When I click on Inbox I get the list again but it indicates that the email I clicked on before has been read.
I thought maybe it had something to do with popups so I made sure that att.net was allowed.
I have no idea what is causing this problem. Anyone know?
Thanks for your help.

 

It should not matter if the mail has been read or not. I access, sometimes my Yahoo mail at the website, and some is read, and some is not, and, you can see from the headers, which are bolded, if unread. I did double check, and read mail came up.