In the "repository" tab when you first boot up the game, does it show up "0 our of 300 mods" or 0 out of 0 mods"?
The same thing happened to me. This is because all my mods were in the steam folder (steam/steamapps/common/beamng.drive/vehicles or whatever) There's another folder in "my documents" called beamng, either put the mod zips in the mods folder or just use the existing vehicles/maps folder in there.
I keep and will keep saying: Please do not install your mods in the Steam folder. You could lose them if an update is our or Steam is feeling generous. Use the correct folder (ie. Documents/BeamNG.Drive) https://wiki.beamng.com/Installing_Content#Installing_Resources_.28Manual_Method.29 (NOTE: If you use the 'Levels' or 'Vehicles' folder, which are not designed for mods, but would still work, you still risk of getting your mods removed if you press the 'Clear Cache' button in the launcher) (NOTE2: It actually doesn't delete anything, it moves them into Documents/BeamNG.Drive/backup)
I got the steam folder location from the "introduction to vehicle creation" wiki page, which seems to be clearly outdated. Having used that to make my first car, it was implied that was the best location for addons, and it did work at the time. https://wiki.beamng.com/Introduction_to_Vehicle_Creation
