Welcome to Zoo Admin.
I do not know what you mean by your game not loading back up.
There are many possible causes for a game to crash. The more information you can give, the better. For example, what are you doing when the game crashes? Does it crash at the same place every time? Does it crash on the same game date every time?
Hopefully you did not remove a ".dll" file that should have stayed. Also, the ".dll" files for some older buildings can cause sporadic crashes. Hopefully you did not run any "patch" programs from older downloads. Hopefully you do not have any user ".dll" files that are larger than 1.8 mb.
If the ".dll" files are as they should be, then you might have to remove the user ".ztd" files that you installed. Then try them one at a time and test them in Zoo Tycoon. That should indicate which ".ztd" file, if any, is causing the problem.