Usually this means you simply need to grab the latest V3 Update from our website at http://www.run8studios.com/updates_dlc.shtml

Depending on the DLC being installed, the pack might be newer than the current version of your sim, and your sim doesn't contain the necessary programming to make that content appear properly. Installing the latest V3 Update of course ensures all of your DLC will show up fine.

Another possible cause is you simply biffed the installation location. If your V3 is located in its default location, all you ever need to do is "next" yourself right thru any V3 DLC installer.

If your V3 is in a non-default location, you will need to specify that location when prompted by the DLC installer.

If you are unsure of your location, you can right-click V3's exe and Windows will show you the proper path.

Run8 V3's default location is:  C:\Run8Studios\Run8 Train Simulator V3