There are problem in reindexing in magento many times due to number of factors:

  • The number of products
  • The number of store views
  • The apache/lighttpd timeout setting
  • The php.ini maximum execution time & script input time
  • The lock file is still place from the previous time can preventing it running again

one more thing VPS or dedicated server is must have for Magento.

here i paste the trick/tips for the same.

First of all increase your execution time value from the .htaccess

 # php_value memory_limit 64M  
   php_value memory_limit 128M  
   php_value max_execution_time 18000

Now open your shell/terminal:
go on upto “public_html/app/shell”

use “ls -l” command, to list out the files.
there is one indexer.php file in the list.

Commads:

  php indexer.php --info (Will shows list of allowed indexers)   
  php indexer.php --reindex all (Reindex data by all indexers)

If you wish to reindex one by one then use following commands:

 php indexer.php --reindex catalog_product_attribute (Reindex Product Attribute)   
  php indexer.php --reindex catalog_product_price (Reindex Products prices)

and so on…..

If you don’t have SSH (Command Prompt) access then try with following script;

 <?php  
 require_once 'app/Mage.php';  
 $app = Mage::app('admin');  
 umask(0);  
 for ($index = 1; $index <= 8; $index++) {  
     $process = Mage::getModel('index/process')->load($index);  
     $process->reindexAll();  
 }

Save file with reindex/php and run go on browser and run it like: http://yourdomainname/reindex.php

Hope this helps,
Do you have any tips? Post them in the comments and I’ll add them to the list!