You need to check the defaults in Options > Editing > Formatting on both versions of Windows. As your paragraphs say “No style” they must be using the font defined there.
Note, I’m on Mac, but that’s the first place I’d look.
Dumb question: Has the font been installed in Computer C? The font is not carried with the project; it has to be installed on the machine for Scrivener to use it.
Have you chosen that font you want to use as the default font for Scrivener? File - Options - Editing - Formatting: then choose the default settings for your chosen format. One of the choices is the font you wish to use. This choice will affect all future new documents until you change it (my advice: set it once to your default font and forget it).
You can limit your choice to a single project, if you wish, by using Project - Project Settings - Formatting (down the left of the dialog box), check the box for Use different formatting, and set your choices in that dialog box (it looks like the Editing formatting dialog box; it’s just limited in scope to that one project). This only applies to future new documents; existing documents will need to be reformatted manually.
This will only apply the project formatting choices to that project. In such a case, default formatting information is somewhere in the project files. That project should open with the font it was saved with, so long as that font is installed already on the PC it’s being opened on.
