Also you should do this, try to Clear your browser's cache
1)For that you need to Close the mail page
2)Click Start > Control Panel > Internet Options (or on Internet Explorer toolbar click Tools > Internet Options) and delete Cookies, Temporary Internet Files, and History.
If you are using new Yahoo mail , you should switch back to classic mail for now
Go to this page -->
Here, at the top of the page there's the option "Do you really want to opt out?", click Yes and you will be switched back to Yahoo! Mail Classic.
Try this much first