I found out what was wrong: I will still logged in yahoo at my work so when I logged from home yahoo must have thought somebody was trying to hack into my account.
Nope there is definately something problem at their (yahoo) end because now a days so many times unable to view my yahoo mail account. Currently i am already log in (it show me on main page) but when i click on mail icon no pages appear for me.
Are you sure that isn't a browser issue? Or worse, you can also suspect that someone is "regularly" checking your email from a "different location", and when that happens, you are getting "session expired" messages on screen.
I think it's nothing strange though. Yahoo will have this kind of problem now and then... As long as you're not using Yahoo for important emails (I wouldn't recommend that), you'll soon get used to it.
That stands for ALL free email services, including Gmail. If you are using it to store important information and sensitive data, you're doing it at your own risk. This is what Google say: I did not search Yahoo's terms but I doubt that they have a different position in this case either.
I don't believe anybody uses it for important mail but they do use it to communicate with family and friends. Somewhat important.