Hi Henk,
If you are referring to the font used for Text objects in the View window, you can set the default font by editing the TextModelDefault object and setting the 'FontName' input. The easiest way to do this is to drag and drop a Text object onto the View window, and click the 'Edit DisplayModel' button in the button bar. Now click the dropdown menu button for the 'Font' field in the button bar. This will show a dropdown menu containing all the installed fonts.
However, if you are referring to the font shown in the Input Editor and the other tool windows, these depend on the fonts provided by the Java installation. If this is the case, then the two computers probably use different versions of Java, and the solution is to re-install the version that worked correctly on one of your computers.
Harry