Not even close to enough information to address your problem.
The wizards here need to know what version of Trainz your running, what you have tried so far, the system you're running, whether this shows up with other sessions, what monorail assets you have loaded, does the demo run correctly, and anything else you think may or may not be helpful to understand your problem.
To borrow from JFE (sorry for stealing thunder), the monorails are working for loads of other people. That's not meant to belittle your problem, just to point out that it isn't generic or common. As a community, we are willing to help but we need something to work with.