My answer is similar to Mani's. I also have a complicated screen setup (docked laptop, logged into a Virtual Machine, viewed on separate dual monitors) and I believe the Item Description Window is actually opening, just not within the view-able screen space.
An old post on GeoNet explains the fix for ArcMap 10.0 back in 2010: https://community.esri.com/groups/technical-support/blog/2010/08/03/in-arcgis-desktop-10-item-description-launched-from-the-arcmap-table-of-contents-data-item-description-doesn-t-work
Instead of deleting or replacing the string in the registry (I have not found a zipped download of the default registry entry for the current versions of ArcMap), I just edited the "WindowsPos" string to be "0,0,0,0". This successfully caused the Item Description Window in ArcMap to open in the upper left hand corner of my main monitor.
For me on Windows 7 using ArcMap 10.4, this is located @ HKEY_CURRENT_USER\SOFTWARE\ESRI\Desktop10.4\ArcCatalog\Settings\DescriptionWindow
You can access the Registry Editor utility by typing "regedit" into your start menu. Start the executable, navigate to the folder for your version of ArcMap, double click the "REG_SZ" (string) file, and type "0,0,0,0".