Hi sharmila,
Run the below php script in magento root folder for any error or else script will run without even timeout also.
< ?php
require_once('app/Mage.php');
umask(0);
Mage::app();
error_reporting(E_ALL);
ini_set('display_errors', 1);
ini_set('max_execution_time', 172800);
ini_set('memory_limit', 1024000000);
echo "start";
$indexer = Mage::getModel('index/indexer')->getProcessByCode(‘catalog_url’);
$indexer->reindexEverything();
echo “end”;