Sorry Ahmed, that was really badly said. What I meant was has the Algebra filter been activated? There is no settings page for it. I have always ensured both were operating in their default settings before doing anything else. In the TeX Settings page, the three text boxes at the end of the page need paths to the related tools in them if you are using a different TeX tool than the fallback mimetex.
mmm Agreed, Marc, but not everyone can install MathJax, permissions are still needed and if the admins have no interest in doing so, it is difficult to get them to move. (Personal experience.) The fallback should be active, so why is that not working? Could someone have botched an installation of something like LiveTeX? I have done that and didn't get it working until I made sure the paths in the Tex Filter Settings page were right - not what I thought they were. And i still do not understand why the fallback was not working.
Try adding filter/tex/texdebug.php and see what you get as a result.
The other thing is where are you writing the equation? If it is in a question it might be that the question module is not rendering it properly.