Could be a few things.
Has the code loaded properly? It may be that there is an error in the code and it has stopped loading and warns you with a message in the ticker window.
Could be you are using the demo version (no licence) and the line limit is coming into effect, in other words you may have a displayed toolpath but if your code is very large you may only be seeing a small part of the toolpath on screen and that part may be so small it is hardly visible.
You may have the machine set up in metric units and the code is Imperial units and thus the tool path is tiny.
Could be your code is way off screen because of the current coordinates in the DROs and the codes position.
If you attach both your xml and code maybe the problem can be found.
Hood