I could get the sign in page, then if i said to check mail I would get a blank page. If i hit back I would get to [url]www.yahoo.com[/url], but as me already signed in. I went to my Yahoo. then click My account [in upper left corner after your screen name] it'll ask you for your password again, and then let you access your profile. in lower righthand column click on Mail to look at mail options. then scroll down that page until you see
Mail Shortcuts

* Check Mail Ctrl+shift+C
* Compose Ctrl+shift+P

* Folders Ctrl+shift+F
* Advanced Search Ctrl+shift+S

* Options
* Help Ctrl+shift+H

click on check mail link [the actual shortcut keys don't work, but the link does]

tell me if it works for you