I checked all the connections were tight

I used knoppix live cd and booted the system and got the partitions in that hard disk drive

I also referred some sites, they says that my lilo.conf file need to be changed. some other sites says that, If an initrd image is missing or that image does not include suitable kernel modules to access the ext3 filesystem on the partition, an error message (Linux Kernel panic: VFS: Unable to mount root fs) will be displayed

Thenks for your suggestions

There's a cool little tool that I think will help you. Download and install Linux::Bootloader. For example:

#!/usr/local/bin/perl

use strict;
use warnings;
use Linux::Bootloader;
use Linux::Bootloader::Grub;

my $config_file = '/etc/grub.conf';

my $bootloader = Linux::Bootloader::Grub->new($config_file);
$bootloader->debug(3);
$bootloader->read($config_file);
$bootloader->print_info('default');
[download]

If you are not sure whether you have Grub or Lilo, then, from the command line, you can run the "boottool":

boottool --bootloader-probe

and it'll tell you exactly which bootloader you are using.