we don't use lync, cant see others content when the share with windows 8.  its ok,we use skype.  why?  and how can it be stopped short of deinstalling lync?

Are you saying that you don't use Lync at all, but it asks you to login? If you don't use it and don't want to remove it I'd suggest making it not start with Windows

You can do this by selecting (from within the client Tools (Alt+T), Options, Personal, Uncheck "Automatically Start Lync with Windows"

If that doesn't work are you able to post a screenshot of the login prompt you are getting?

If no one click on the Lync Client, lync will not start automatically.

If the lync Client starts, you have to disable th personal Settings to start Lync with Windows.

Here ist the link with the registry entry to stop autostart of the Lync client.

http://blogs.technet.com/b/rischwen/archive/2013/06/20/lync-2013-client-auto-start-registry-key.aspx