Did you recently upgrade PHP?
If so, the default setting is for register_globals=off.
Try this...
<?php
//test.php
if ($_POST['go']) {
print "hello world";
}
?>
<form method="POST" action="text.php">
<input type="submit" name="go" value="go">
</form>
If it works, then you have register_globals turned off.
You will need to use the super-globals to access your passed variables
$_SERVER,$POST,$GET,$COOKIE,$SESSION.
For more info Predefined variables
HTH