There are some reports that the console in PDQ Inventory 3.1 fails to start. This will happen in only a few rare circumstances. The issue has to do with certain patches to .NET 4.0. If you are running PDQ Inventory on a system that has the following versions of the CLR.DLL file you will need to update .NET 4.
If the console is running on Windows 7, 2008 or Vista then we recommend that you either install all patches for .NET 4 (including the optional patches) or just install .NET 4.5.2. If the console is running on XP or 2003 then you will need to install all of the .NET 4 patches. If this still doesn't fix the issue you will need to uninstall and reinstall .NET 4 (we still recommend installing all of the patches as well).