It could be a couple of things. If you don't have lots of feeders, you may be depending on the turnout to route power further down the track. If that's the case, you may only be getting power when the turnout is aligned the right way. Or, if something is wired incorrectly, including a lack of insulators in some cases, you could be getting a short when you throw the turnout the wrong way.
Put a meter across the two stock rails of the turnout, or just use a small light bulb. If the meter indicates voltage in both positions of the turnout, then you do not have a short, but if your voltage goes to zero when you throw the turnout one way, you've found your problem.
If you are forced to use a light bulb, get a meter. A cheap one, even one of the ultra-cheapies from Harbor Freight, will do the job.
It takes an iron man to play with a toy iron horse.
N scale: Turnout at one part of the layout seems to control train movement at other part. Engaging the turnout lets the train (at the other end) move again. What needs to be done?
Sid