Have you tried to login using Firefox browser to see if you can login in your yahoo account?
Or you can try to install any program that will allow you to login in Yahoo services e.g. eprompter email checker from eprompter.com, yahoo messenger
If you still can't login using another internet application, please go to http://help.yahoo.com/l/us/yahoo/security/ then choose "Account Security" to get help in changing your password or to check if your yahoo login has been hacked or not.
Recently, since I reninstalled WinXP Pro on my desktop, I have been unable to login to Yahoo. In other words, the window that follows the login page keeps telling me that I have entered an invalid login. It seems like a hacker has either disabled my PC's submission of the login or has otherwise hacked the Yahoo login.
What may be done to fix this problem?