Silverlight 4.0 is automatically installed as part of running setup for Lync 2010 RTM desktop client. If for any reason the former is missing or corrupted, launching Lync may appear that nothing is really happening i.e. no visual cue of the application loading.
Opening Windows Task Manager may reveal that the communicator.exe *32 process (for Microsoft Lync 2010) is indeed already running. Nevertheless, waiting a couple of minutes more may not change the situation. Should you terminate or kill the process and restart Lync 2010, an error message similar to the following may appear:
You must install the latest version of Microsoft Silverlight before you can sign in to Lync. Click Install to download and install Silverlight.
[ Install ] [ Close ]