Windows Not Assign Drive Letter To USB External Drive

It is convenience to use USB portable external hard drive to backup or transfer files to others. I'm using PATA and SATA USB hard drive enclosure for backup. After transferring files into few USB external hard drives, Windows (Windows Vista or Windows 7) are not showing my USB external hard drive in "Computer".

By right click "Computer" and select "Manage", click on "Disk Management", the USB external hard drive appear as "RAW" and not accessible under file explorer.

It still not accessible by safely remove the USB drive and plug it back. After google around, I'd found out the reason why Windows are not assign drive letter to my USB drive.

It is solved by enable a Windows's DiskPart tools feature called AutoMount under command prompt.

1.) Click on the "Start Orb" - "All Programs" - "Accessories" - "Command Prompt"
2.) Type diskpart, press enter.
3.) Type automount enable, press enter.
4.) Type exit to end diskpart tool.
5.) Safely remove all connected USB drive and and plug it back.