Hi
What version of VP are you using and is it licensed? Not sure what happens with the unlicensed version regarding the stock sounds but just right click the clip area and you should see this menu...

Select Add Audio from NCH Sound Effecr Library This connects to the server and open a window of sound...

Simply browse the lists and select something and then Download it.
It downloads from the server and arrives in the Audio Clip bin.
That's what should happen! You could try a reinstall or try the latest version Save your project first. Put your original vpsetup.exe file and your registration code somewhere safe first. Upgrades are free for 6 months.
https://www.nchsoftware.com/videopad/versions.html
Nat