Steve check your local folder. To get to it unhide all folders and protected files then go to C:/Users/your name/AppData/Local folder and look for the N3V Games. It should still be all there, what happened is that the new install created a new local folder that does not have your older data, and you need to point Trainz to your older folder, there is online help for doing that.
When you find it back it up to an external Drive to protect it, you need to always protect your Data just in case of a PC or Hard Drive Failure.
Do not forget to reset your Folders to hidden after you find it and get it saved, or moved.