Contents of External Hard disk cannot be accessed

I have a seagate external USB hard disk(500 gb). One day it was working fine and the other day when I plugged it into my Windows OS, it was listed as Local Disk instead of Expansion Drive which is its usual name. Also, no information about the disk was displayed(like the one which says 'x GB free of y GB'). If I click onto the Local disk, the windows explorer stops responding.

So, I turned to Ubuntu for help. When I inserted the disk into the USB port, the disk was listed as Expansion Drive but it didn't open which it should have automatically. So I clicked on the Expansion drive to mount it and the following error came:

DBus error org.gtk.Private.RemoteVolumeMonitor.Failed: An operation is already pending

After waiting for much long, it said that it couldn't mount the drive with the following error:

    DBus error org.freedesktop.DBus.Error.NoReply: Did not receive a reply. Possible causes  
   include: the remote application did not send a reply, the message bus security policy 
    blocked the reply, the reply timeout expired, or the network connection was broken.

Now, I checked the fdisk -l option in the shell and this is what it printed as output:-

Disk /dev/sda: 500.1 GB, 500107862016 bytes
255 heads, 63 sectors/track, 60801 cylinders, total 976773168 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: 0xd610bb10
Device Boot Start End Blocks Id System
/dev/sda1 * 206848 157573119 78683136 7 HPFS/NTFS/exFAT
/dev/sda2 157573120 876421119 359424000 7 HPFS/NTFS/exFAT

/dev/sda3 876423166 976771071 50173953 5 Extended
Partition 3 does not start on physical sector boundary.
/dev/sda5 876423168 884234239 3905536 82 Linux swap / Solaris
/dev/sda6 884236288 976771071 46267392 83 Linux

Disk /dev/sdb: 500.1 GB, 500107859968 bytes
255 heads, 63 sectors/track, 60801 cylinders, total 976773164 sectors
Units = sectors of 1 * 512 = 512 bytes
Sector size (logical/physical): 512 bytes / 512 bytes
I/O size (minimum/optimal): 512 bytes / 512 bytes

Disk identifier: 0x569f2049
Device Boot Start End Blocks Id System
/dev/sdb1 63 976768127 488384032+ 7 HPFS/NTFS/exFAT

Also, I used GParted. It gave me the complete info about my hard disk. I attempted data rescue using GParted but no file systems could be found there. can anyone tell me any other way to get my data back from that hard disk(Few videos and docs are really important). Thanks in advance.

Update:
I am now able to mount the disk. But when I open the disk, no folders are visible, though a space of 298 gb is being utilised. What should be done?