I installed the day before a set of packages for GCC-4.8.2 compiled on my machine Ubuntu 12.04. After the installation of the 52 packages I got some broken dependencies with i386 libraries (Multi-Arch) I did not compile at that time as I had compiled the amd64 version. As soon as the Update Manager displayed the red icon (broken packages) I noticed that the Unity Dash was unable to show any applications. I shut down my PC for the night in that state. The following day I fixed all the i386 (Mulyi Arch) libraries. Then the Update Manager was working again, but the Unity Dash is still unable to show any application ...
I tried to purge and re-install
unity-lens-applications then restarting the PC. That didn't change anything to the Unity Dash behavior. It looks like there is somewhere a bug or some configuration on which it relies is corrupted. Everything else is working fine so far.