Help, i am setting up an "n" gauge layout and i seem to be encountering a short circuit that is causing my power pack to go into protect mode. Suggestions for trouble shooting please

Does your layout have a reverse loop?

Or did you leave a metal tool laying over the track? 

Or have you tested it without the locomotive, to see if the locomotive is the problem.

Or, as can sometimes happen, at either end of the power feed to the track, do you have a bare stranded wire where one loose strand from one wire is touching the other wire?

Or, is some freight car causing the problem?

All good questions.  Would like to know what you eventually found as the culprit.