One of my friend was unable to mount a 250 GB external hard disk and the disk which has NTFS file system.
With help of my friend google, I found a driver called NTFS-3G which supports read/write NTFS driver for Linux, Mac OS X, FreeBSD, NetBSD, OpenSolaris, QNX, Haiku, and other operating systems.
it provides safe and fast handling of the Windows XP, Windows Server 2003, Windows 2000, Windows Vista, Windows Server 2008 and Windows 7 file systems.
The ntfs-3g packages comes pre-installed with the newest versions of Ubuntu, but you still need to install ntfs-config
sudo apt-get install ntfs-config (or) ntfs-3g
sudo mkdir /media/sdb1
sudo mount -t ntfs-3g /dev/sdb1 /media/sdb1
ls -la /media/sdb1
Now you can start 250 GB external hard disk and the disk which has NTFS file system.