Peculiar. What are your PC's specs: CPU/GPU/RAM? You are certain that nothing is muted and that volume controls to the left of each audio track are fully to the right?
If you are running Windows 10, right-click the 'speaker' icon at the bottom-right of the window and choose OPEN VOLUME MIXER. Scroll the display to the right if necessary and see if the volume is turned all the way down on the Videopad slider. If so, slide it up to match the other entries.
As a last resort est this version. Does it do the same? Retain your registration, if yours is a licensed version.