I'm running Kali, which is based on Debian.  Recently, after some updates, the computer would only boot to a text prompt; no GUI.  I found that, somehow, I had a more recent version of a Gstreamer-plugins library than GDM3 could run on.  I removed the library, then re-installed GDM3, letting it choose whatever libraries it depended on.  That worked, to a point.  It boots to the GUI now, and gives me a login prompt.  I enter my username and password successfully, but then I get a solid-color background, a mouse cursor, and nothing else; no icons, no status bars, no menus, no apparent response to mouse clicks.

My guess is I still need to re-install something else that runs on top of the display manager, but I don't know what.  Any ideas?