If you are unable to login to your account then there could be various possibilities for that problem. Some of the common reasons for these problems are your account login details has been changed specially your account password, the browser you have installed in your machine has gone too old or it is not working fine, also it can happen that you have forgotten your login details or your account has been hacked. Therefore, never try to fix this problem your own. Instead of that call to Yahoo tech support phone number and get assistance from them to fix problem.