by Luis de Vasconcelos.
Reinstalling it a third time probably won't fix the problem. Rather, add the following code:
@error_reporting(E_ALL | E_STRICT);
@ini_set('display_errors', '1');
$CFG->debug = (E_ALL | E_STRICT);
$CFG->debugdisplay = 1;
above this line in your Moodle config.php file:
require_once(dirname(__FILE__) . '/lib/setup.php');
That will enable the debugging function in Moodle. You can then check the error messages that get triggered during the installations to see what the real problem is.
See http://docs.moodle.org/26/en/Debugging for more info on how to setup the debugging options.