boot - Lost disk space after switching to Ubuntu from Windows

I am new to Ubuntu and was really excited to try it. I did my home work before installing Ubuntu on installation topics. So, I'm fairly knowledgeable about systems.

1. Hardware: Dell Inspiron 14R (N4110) came with Windows 7 pre-loaded note that my Storage Size is 750 GB.




2. I wanted to remove Windows completely (so data back-up was done to external HDD) and installed Ubuntu 14.04 LTS by following Ubuntu installation pages and specified "Replace Windows 7 with Ubuntu" while installing from boot using "Ubuntu DVD"




3. Followed all the prompts provided and installation was done.

PROBLEM: Meanwhile I was thinking that this installation will format my hard disk, remove all the Windows files, partitions and data, so that my disk space would be around 750 GB again. But, now the available disk space is 290GB something.

What happened to rest of the disk space?
How can I recover it back? If not easy, even at the cost of reinstalling Ubuntu!!

This details might help you -

"boot -info" analysis of my system

gparted screen shot : in this link here

fsdk -lu report:

ramesh@ramesh-Dell-System-Inspiron-N4110:~$ sudo fdisk -lu
[sudo] password for ramesh:
Disk /dev/sda: 320.1 GB, 320072933376 bytes
255 heads, 63 sectors/track, 38913 cylinders, total 625142448 sectors
Units = sectors of 1 * 512 = 512 bytes
Sector size (logical/physical): 512 bytes / 4096 bytes
I/O size (minimum/optimal): 4096 bytes / 4096 bytes
Disk identifier: 0x0004acbc
   Device Boot      Start         End      Blocks   Id  System
/dev/sda1   *        2048   616968191   308483072   83  Linux
/dev/sda2       616970238   625141759     4085761    5  Extended
Partition 2 does not start on physical sector boundary.
/dev/sda5       616970240   625141759     4085760   82  Linux swap / Solaris
ramesh@ramesh-Dell-System-Inspiron-N4110:~$

How should I proceed?

Your boot info on line 57 clearly shows that your system has an ata-ST320LT007 hard disk. If you've bought this system as a 750GB system, there was a problem on the manufacturing line assembling your system (or you've been ripped off).

Take the machine, pack it in the original boxes and return it to the store together with the below info

lrwxrwxrwx 1 root root  9 Jan 31 22:37 ata-ST320LT007-9ZV142_W0Q07XXE -> ../../sda

and a copy of the hard drive specifications on the Seagate web site and ask for a refund or for another machine.