Install Code Help

[Twilkey]

I am working on a mod and I am having trouble with install code. For some reason it wont alter the user table and it wont create a new table.

<installcode><![CDATA[$query = "ALTER TABLE ". TABLE_PREFIX . "user ADD imagewtf_url integer default 250";
$db->query($query);

$query = "CREATE TABLE imagewtf_settings (settingid integer NOT NULL PRIMARY KEY auto_increment,
settingname text, switch1 integer, switch2 text)";
$db->query($query);

$query = "INSERT INTO imagewtf_settings (settingname, switch1, switch2) VALUES ('imagewtfactive', 1, NULL)";
$db->query($query);
$query = "INSERT INTO imagewtf_settings (settingname, switch1, switch2) VALUES ('allowedusergroups', 0, '2, 5, 6, 7')";
$db->query($query);]]>
</installcode>

My Table Prefix in my config file was left blank. When I tried to edit it, my whole forum went down until I change it back.