Recommendation 
 I would recommend you use mysqli ( http://php.net/manual/en/book.mysqli.php ) which is an improved version of mysql
 Quick Fix 
 Full Details of all possible reason available at 
 http://www.somacon.com/p109.php
 Let me know if you need more assitance 
 Last Resort 
 Re install PHP53
 Remove the 5.1.x PHP Packages:
  yum remove php php-* 
 Remove the 5.3.x PHP Packages:
  yum remove php php53-* 
 Install PHP5.3
 yum install php53-cli yum install php53-common yum install php53-devel (If you need development support) yum install php53-gd yum install php53-mbstring yum install php53-mysql yum install php53-soap yum install php53-xml yum install php53-xmlrpc yum install php53-bcmath yum install php53-snmp 
 Restart Apache 
 Service httpd restart 
 yum search
   
phpinfo()return? Does it include info about MySQL? Server restarted?'--without-mysql'i have restarted my server