Black hot wire coming into 50amp breaker not working

[Christeen]

Black wire has no electricity coming into the breaker. The other wires are fine. Does anyone know what can be the culprit? Only ½ of the outlets worked. Not including AC, or fridge, kitchen, etc. - Thinking converter? Only I don’t even know where it is. 2004 Keystone Montana 3290RK - might not be the exact model.

[BB_TX]

First place to check is power coming in from shore power. Are you at a new site? Make sure your power cord is firmly connected to the shore power outlet and the other end firmly connected to your trailer.
You need to troubleshoot using a voltmeter. Verify you have 120 vac on both hot pins at the shore power outlet. If not then a shore power problem.
If so, then plug your cord into the outlet and disconnect the cord from the trailer and verify you have 120 vac on both hot pins of the trailer end of the power cord. If not then a power cord problem.
If so then trailer troubleshooting begins.