Changing the theorem's title style

I need to change the style of the theorem title ( bold and no ponctuation after the title) :

\documentclass[french,a4paper,12pt]{report}
\usepackage{babel}
\usepackage{graphicx}
\usepackage{amsmath,amsfonts,amstext,amssymb}
\usepackage{times}
\usepackage{setspace}
\usepackage{Lettrine}
\usepackage{fancyhdr}
\usepackage{multirow}
\usepackage{pslatex}
\usepackage[T1]{fontenc}
\usepackage[latin1]{inputenc}
\usepackage{array}
\usepackage{enumerate}
\usepackage{color}
\usepackage{version}
\usepackage{newcent}
\usepackage{nestochp}
\usepackage{anysize}
\usepackage{amsthm}
\makeatletter
\makeatother
\theoremstyle{remark}
\newtheorem{Def}{Définition}
\newtheorem*{pre}{Preuve}
\newtheorem{The}{Théorème}
\newtheorem{Lem}{Lemme}
\newtheorem*{Rem}{Remarque}
\newtheorem{pro}{Proposition}
\numberwithin{equation}{chapter}


When I use the code above I got no ponctuation after the theorem's title but the font is not bold.

How can I fix this?

Since,judging by the use of the remark style in your example code, you want boldfaced head, no punctuation after the head and normal font for the body, you can easily define a new style with those requirements:

\documentclass[french,a4paper,12pt]{report}
\usepackage{babel}
\usepackage{amsthm}

\newtheoremstyle{mystyle}% name
{\topsep}% Space above
{\topsep}% Space below
{\normalfont}% Body font
{}% Indent amount
\theoremstyle{mystyle}
\newtheorem{Lem}{Lemme}

\begin{document}

\begin{Lem}
A test lemma.
\end{Lem}

\end{document}


If you only want theorems with bold title and no punctuation, this should do it:

\documentclass{article}
\usepackage[utf8]{inputenc}
\usepackage[english]{babel}

\newtheorem{theorem}{Theorem}

\begin{document}
\begin{theorem}
This is a simple theorem with bold title an no punctuation after the title.
As simple as it gets...
$$a^2+b^2=c^2$$
\end{theorem}
\end{document}

• Welcome to TeX.SE! You may have missed the fact that the OP loads the amsthm package. (Admittedly, he/she didn't make it easy to notice this since the example also loads quite a few other packages that are irrelevant for the issue at hand!) Your answer will have to be modified in order to give the desired result with amsthm. Incidentally, the use of $$ in LaTeX documents is severely deprecated; see, e.g., Why is $...$ preferable to $$ ... ? – Mico Oct 25 '14 at 22:11