If error reporting is set to E_ALL then this
if($_GET["cmd"]=="edit" || $_POST["cmd"]=="edit")
would both report an undefined variable. Check also the setting for display_errors() it should be set to 'on'.
You can check the ini settings using phpinfo(); it's possible you're looking at the wrong ini file. phpinfo() will show the path under "Configuration File (php.ini) Path "
print_r($_POST); will display all the posted variables so you can see what is being received after the form is posted. You say the vars are updated to empty so you need to see where that values are being lost. First check they are received by the script and look at you would expect. You can add
echo '<pre>'.print_r(@$_POST).'</pre>'; to the top of the script. You'll see
when the page first loads as the POST array is empty.
Submit the form and you'll see the submitted values displayed.
Then echo the query to the page and see who it looks. Copy it and run it on a command line like putty and see if you get any errors.