You'll have to be a bit more specific. What exactly is happening, or not? How far into the start up process do you get?
What does the jetlog file say?
Did anything out of the ordinary happen the last time Trainz was working? When it shut down?
Even if the program is toast, the data you created and saved should still be OK. Before doing anything else, copy your whole "world" folder to another place, another drive if it is available. For 2006, I would also copy the "local" folder. Those more familiar with 2006 better guide this issue. Good luck