Dear chayapa.prempree,
We recently wrote to tell you that we are now retiring older versions of Skype and you'll not be able to sign in until you update. It looks like you haven't updated Skype yet. If you're on the latest version of Skype for Windows, please disregard this mail.
The new version comes with improved performance, the latest features and security updates so you'll get the best possible Skype experience. Simply download the latest version now and sign in to continue using Skype.