From time-to-time you may have problems in Visual Studio with things like changing the Microsoft account. To easily reset VS 2013 user settings allowing you to sign in again you can use the following command-line from the Developer Command Prompt:
This is fine for VS Pro or Ultimate but not Express because devenv does not exist!
Instead try the following fro VS 2013 for Web:
And this for VS 2013 for Windows:
All the different Express IDEs are located here:
C:\Program Files (x86)\Microsoft Visual Studio 12.0\Common7\IDE