Comment 2 for bug 1421222

Possible steps to further investigate on the affected system (if non of the two above explanations match:

1) quit all running Inkscape processes
2) rename the Inkscape user profile
 %APPDATA%\inkscape
3) launch inkscape again (it will recreate the Inkscape preferences with default settings)
4) Now test whether the 'Export PNG Image' opens visible with the new preferences (docked at the right side of the current Inkscape document window).
5) If new preferences make the export dialog appear, please attach the old (saved in step 2) and the new preferences file to this report
%APPDATA%/\inkscape\preferences.xml