From my experience, there are 2 possibilities:
Have you tried to format your computer?
Have your tried to disable your anti-virus for the installation?
In the company I work, 4 computers installed it with no problems, but other 2 had exactly the same issues you described (running on 64-bit Windows 7).
We had to format these 2 computers, and after that the installation had no problems.
If you are in a network (like I am, at work), try installing with "Run as administrator" or calling the network manager to give your computer full permission to install softwares.
We didn't understand the problem though, maybe some messed up Microsoft's .NET Framework package.
Another thing we noticed, before we formatted the computers, the installation was too fast (it finished, but too fast), so I think something was blocking part of the installation without the installer noticing it (resulting in missing files like the qgis_core.dll).
I started experiencing this issue today with QGIS 2.18.12 (Las Palmas) on WinServer 2008r2 in mid-session (for which I have no explanation, although Firefox also hung, whilst a number of other applications continued to run happily).
Thereafter, QGIS start-up hung at 'setting up the GUI'
The issue appears to be that the path to %OSGEO4W_ROOT%\apps\qgis\bin gets lost (which is where the GUI library qgis_gui.dll is stored). I managed to get QGIS to run by:
- Run OSGeo4W Shell (as described above), either from start menu, or by running [QGIS-installation-folder]\OSGeo4W.bat
extend the PATH environment variable for the shell:
path %OSGEO4W_ROOT%\apps\qgis\bin;%PATH%
Run QGIS from command prompt in OSGeo4W Shell (again as above):
qgis
(and now for the weird bit) try running it from the normal shortcut - for me QGIS has started working again.
Good luck!
Best Answer
I think this recently fixed issue is related to your post:
Long term release installer 2.14 installs 2.16 and makes 2.16 default version