makeindex doesn't use indexed words

Question

When I use makeindex and try to index a word using

Hello \index{World}

the entry in the generated \printindex looks like

indexfile, 7

instead of

World, 7

-- This issue also happens when using World\index{World}.

The error seems to be somewhere before creating the .idx, as it looks like this

doc.idx

\indexentry{\@indexfile |hyperpage}{7}

doc.ind

\begin{theindex}

  \item indexfile , \hyperpage{7}

\end{theindex}

Used packages

\usepackage{geometry}
\usepackage{ngerman}
\usepackage[latin1]{inputenc}
\usepackage{fancyhdr}
\usepackage{makeidx}
\usepackage{showidx}
\usepackage{graphicx}
\usepackage{textcomp}
\usepackage{setspace}
\usepackage{listings}
\usepackage{color}
\usepackage{hyperref}

Answer 1

That is not possible as could be seen in this example:

\documentclass[ngerman]{article}
\usepackage{geometry}
\usepackage{babel}
\usepackage[latin1]{inputenc}
\usepackage{fancyhdr}
\usepackage{makeidx}
\usepackage{graphicx}
\usepackage{textcomp}
\usepackage{setspace}
\usepackage{listings}
\usepackage{color}
\usepackage{hyperref}
\usepackage{showidx}
\makeindex
\newcommand\Index[1]{#1\index{#1}}
\begin{document}

This is my \Index{world} and my \Index{World}.

\printindex
\end{document}

it creates a correct index:

I run pdflatex->makeindex->pdflatex. You have to create a complete example which shows your behaviour.