When you start the Lync Client and won’t get past “Contacting server..” ,and it never time’s out. It can be worth checking time on client and servers. Other users can sign in to Lync, even on the same PC. It will not help removing Lync client certificate, or reset password. Solution here is to check date and time on Lync server and Client – if it is Office365 it is your Client that has wrong time.