My system don't store session data, anybody can help me!!

In my system i have apache-1.3.17, (i probe 1.3.14 but the problem persist), when i register a variable the session is generatet and a file sess_f5g ... is generated under /tmp but the file is empty size=0, and no data is stored. <?php session_start(); if( !isset( $c)) { session_register("c"); $c = 1; } echo $c . "<br>"; ?> <a href="index.php">reload</A> this example that works fine in other system with the same configuration, don't work in my machine, everytime he say 1. my system is a red hat 6.2 with 2.2.14 and my php is 4.0.4pl1