Problems sharing screen (able to share document and whiteboard) - doesn't seem to be pop-up issue or account issue (can share screen when accessed from my laptop). Help!!!

I can not share my screen (I can share documents and whiteboard) even after having Add-In installed.  When I click on Share My Screen, the window which asks what I want to share (e.g., desktop) does not appear.  Doesn't seem to be pop-up blocker issue. 

I am able to do this on my personal laptop (installing the Add-In did the trick for that).  Have rebooted and it still doesn't work ... at a loss ...