What version of Videopad is being used? Look at the bottom-left corner of the window.
Try this one for now. Ignore any virus warnings. If that doesn't help, come back here.
If you have exported each part, assemble those clips into a new project and then export a final version.
If you have created each part an individual sequence, click the + sign to the right of a sequence tab to open a new blank sequence.
Then, up in the bin (top-left), click the Sequences tab. Drag each sequence to the new sequence on the timeline. When all four are there, export that sequence.