I have the exact same problem. I use IE 9. ATT support indicated yesterday that there are still problems with IE9 and IE10 conflicting with Yahoo/At&T email at Yahoo.com or ATT.com. I was instructed to uninstall IE 9 and re-install IE7 or IE8 after 24 hours. In the meantime I use the following: www.mailyahoo.com and I'm able to open my INBOX by using google chrome for my browser. I did not get an issue number for reference.