windows - External hard disk can be detected but cannot be accessed

I've plugged an external hard disk on my computers. The device has been detected, but isn't shown on explorer. It is the same situation on both windows 7 and windows 10.

Detected / installed because it was shown in control panel > Devices and Printers. Also because I've found it using the list disk command line and it should be the Disk 1 :

Microsoft DiskPart version 10.0.10586

Copyright (C) 1999-2013 Microsoft Corporation.
On computer: TOSHIBA-MINCONG

DISKPART> list disk

  Disk ###  Status         Size     Free     Dyn  Gpt
  --------  -------------  -------  -------  ---  ---
  Disk 0    Online          238 GB      0 B        *
  Disk 1    Online          465 GB   127 MB        *

Unrecognized because it seems that the Partition 2 has unknown file system type. So it cannot be recognized by windows.

DISKPART> select disk 1

Disk 1 is now the selected disk.

DISKPART> list partition

  Partition ###  Type              Size     Offset
  -------------  ----------------  -------  -------
  Partition 1    System             200 MB    20 KB
  Partition 2    Unknown            465 GB   200 MB

Can somebody help me to resolve this problem without clean the data in the hard disk ?

---

Update

I tested the hard disk format type on OSX. And its type Apple_HFS as you can see at /dev/disk2.

Air-de-xx:~ xx$ diskutil list
/dev/disk0 (internal, physical):
   #:                       TYPE NAME                    SIZE       IDENTIFIER
   0:      GUID_partition_scheme                        *121.3 GB   disk0
   1:                        EFI EFI                     209.7 MB   disk0s1
   2:          Apple_CoreStorage Macintosh HD            120.5 GB   disk0s2
   3:                 Apple_Boot Recovery HD             650.0 MB   disk0s3
/dev/disk1 (internal, virtual):
   #:                       TYPE NAME                    SIZE       IDENTIFIER
   0:                  Apple_HFS Macintosh HD           +120.1 GB   disk1
                                 Logical Volume on disk0s2
                                 440DB97F-xxxx-xxxx-xxxx-19AEAC28E415
                                 Unencrypted
/dev/disk2 (external, physical):
   #:                       TYPE NAME                    SIZE       IDENTIFIER
   0:      GUID_partition_scheme                        *500.1 GB   disk2
   1:                        EFI EFI                     209.7 MB   disk2s1
   2:                  Apple_HFS MEMUP                   499.8 GB   disk2s2

Answer

What was the hard drive used for previously? Make sure the hard drive is formatted in NTFS, Fat32, or eXFat so that it is readable by Windows. Windows can't read file systems that are formatted for Mac or Linux. It may also not be mounted.

Guide to mount drives: http://windows.microsoft.com/en-us/windows/mount-dismount-drive#1TC=windows-7