I have a user (OS X 10.6.8 with Lync 14.0.4) who was previously using Lync without problems.  She noted that it took a long time for the app to close when you quit it (which is true for all of us, but it eventually does quit if you give it enough time).  But she grew impatient and did a force quit while it was closing.  Now when she launches it, the Lync menu bar appears but then it stops responding.  No windows open.  In Activity Monitor, the Lync app says "Application Not Responding".