If downloaded parts aren't showing up in LDCad, the first thing to check is that the program is correctly set up to point to your parts library. You set that up under the menu Prefs->LDraw->Search (library) paths.
First be sure that you've saved complete.zip in the correct folder on your computer (the one you've decided to use as your LDraw parts library). Then in the menu above, ensure you have at least an entry for an Official library with that same folder as its location. If you need to browse for it, be sure to select Browse Archive on the top line, as you're pointing to a zip file (a type of archive).
You may find some of the info in this earlier thread useful: https://forums.ldraw.org/thread-27439.html
Roland also gives instructions there on how to reset your configuration, if you're totally lost. That will force you to set up your library location again, so you just find your complete.zip at that time.
First be sure that you've saved complete.zip in the correct folder on your computer (the one you've decided to use as your LDraw parts library). Then in the menu above, ensure you have at least an entry for an Official library with that same folder as its location. If you need to browse for it, be sure to select Browse Archive on the top line, as you're pointing to a zip file (a type of archive).
You may find some of the info in this earlier thread useful: https://forums.ldraw.org/thread-27439.html
Roland also gives instructions there on how to reset your configuration, if you're totally lost. That will force you to set up your library location again, so you just find your complete.zip at that time.