When do you use ninguno?
You use ningun before singular masculine nouns, but what do use ninguno before?
Omitting plural uses as they don't pertain to your question:
ningún is an adjective. (as is ninguna, of course)
ninguno is a pronoun. (as is ninguna)
No hay ninguno. (pronoun, none or not any)
There is none. There isn't any.
Being a negative word it is used in negative sentences such as these. If it's an positve sentence use alguno.
Hay alguno. Hay algún ejemplo.
Also, even though, ninguno is normally used as a quantifying adjective and placed before the noun I also think that it is possibe to use it after the noun where it would be ninguno rather than ningún or ninguna.