The citation is a question mark and the list of reference doesn't appear

Question

I tried a lot of times, but the reference list doesn't appear and the citation in the text is always a question mark. This is my bib file.

\begin{filecontents}{mybib.bib}
@booklet{mwe,
author      = {{S}charrer, {M}artin},
year        = {2012},
title       = {The mwe-Package},
edition     = {0.3},
language    = {english},
lastchecked = {2012-07-12},
url         = {http://mirror.ctan.org/pkg/mwe},
note        = {macros/latex/contrib/mwe}
}

@Book{Renewal,
author = {Breuer, L. and Baum, D.},
title = {An Introduction to Queueing Theory and Matrix-Analytic Methods},
publisher = {Springer},
year = 2005,
}
\end{filecontents}

Next is my tex file.

\documentclass[a5paper]{article}

\usepackage{filecontents}     
\usepackage[numbers]{natbib}  
\usepackage{hyperref}         

\begin{document}
\section{First section}

Minimal Working Example MWE.

citations: \cite{Renewal}, \citep{mwe}, \citet{mwe}, \citep*{mwe}. 

\bibliographystyle{unsrtnat}  
\bibliography{mybib}          
\end{document}

Both of 2 files are from a buddy's answer in the website.