It is possible that you might get into sign in loop when you click sign in, in the yahoo account page. The sign in page will appear again and again preventing you from entering the yahoo mail account. To resolve this problem you have to resend the sign in cookie so that it can be stored in the proper manner in your Internet browser. After this go to signing page and click on sign in as a different user and then click sign in. This should resolve the problem. However, if you continue to face the issue it is always advisable to get in touch with the expert professionals at yahoo customer support by dialing the yahoo help line number.