Thanks for the suggestions. I re-downloaded and re-installed Octave 3.2.3, and seems that my computer just does not behave the same as the older ones. Following your suggestion, the output of gnuplot_binary() after I started Octave is:
ans = C:\Octave\3.2.3_gcc-4.4.0\bin
Then I tried to plot the basic sine function that mentioned when I "doc plot" and I still could not the plot. Please find attached the screen that hopefully illustrates the error message I mentioned.
Any light is much appreciated. Thank you and regards, YF.
error.gif