Recently I faced problem with Skype for Business where I was not able to login. After searching I got to know to change the settings and to change the correct date and Time
Problem was with date and Time in my computer. So I have changed it.
Change Setting in Skype.
Go to Tools-Options.
Go to Advanced Connection Settings.
In here check “Manual Configuration”.
For Internal server name enter “sipdir.online.lync.com:443”.
For External server name enter “sipdir.online.lync.com:443”.
Click on OK and proceed to log in.
Once this was done now I am able to login to skype.