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mint@mint ~ $ sudo fdisk -l

Disk /dev/sda: 640.1 GB, 640135028736 bytes
255 heads, 63 sectors/track, 77825 cylinders, total 1250263728 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: 0xc52b32c4

   Device Boot      Start         End      Blocks   Id  System
/dev/sda1   *        2048      206847      102400    7  HPFS/NTFS/exFAT
/dev/sda2          206848   419411967   209602560    7  HPFS/NTFS/exFAT
/dev/sda3       419411968   629127167   104857600    7  HPFS/NTFS/exFAT
/dev/sda4       629129214  1250263039   310566913    5  Extended

Disk /dev/sdb: 8032 MB, 8032092160 bytes
248 heads, 62 sectors/track, 1020 cylinders, total 15687680 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: 0x20ac7dda

This doesn't look like a partition table
Probably you selected the wrong device.

   Device Boot      Start         End      Blocks   Id  System
/dev/sdb1   ?  3224498923  3657370039   216435558+   7  HPFS/NTFS/exFAT
/dev/sdb2   ?  3272020941  5225480974   976730017   16  Hidden FAT16
/dev/sdb3   ?           0           0           0   6f  Unknown
/dev/sdb4        50200576   974536369   462167897    0  Empty

Partition table entries are not in disk order