a few days ago I decided to update my QGIS 2.14 into a QGIS 2.18.
I uninstalled the old version and installed the new one, normally. Then nothing at all happened when I pressed the icon.
I uninstalled, deleted all registry mentioning old installations of QGIS, reinstalled 2.18, and still nothing.
I tried installing QGIS OSGEO4w, but again, nothing.
I changed the Qgis.bat to add the system folder
PATH %systemroot%\system32; %systemroot%; %systemroot%\system32\wbem
, and nothing..
I really don't know!
Clearly I also tried to install back the 2.14, but it does not launch either.