no plot on Windows

[Francesco Potortì]

I recently needed to install Octave on some Windows systems and havfe a
problem with plotting.

I installed Octave 4.0.0 on Windows Vista.  The default tk toolkit does
not work a window appears with all decorations but for the rest is empty
and does not go away, so you havf to kill Octave.  Happily, doing

>> graphics_toolkit gnuplot

overcomes the problem.

Hoever, on another PC where I had Octave 3.6 installed, which I
uninstalled before installing Octave 4.0.0, it does not work: when
plotting with gnuplot, no window appears and Octave hangs.

Gnuplot 4.6 works: I can see its prompt calling it from the Octave
command window doing

» system gnuplot

I discovered that the uninstallation of Octave 3.6 left something: I had
an old Gnuplot in a user local subdir, and I deleted those directories.
But nothing changed: plotting with gnuplot does not work (it does not
work with tk or fltk either).  When not plotting, Octave works.

I suspect some old dll or something around, but I am not a Windows
expert.  Any suggestions?

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