Usb Drive Does Not Appear In Windows Explorer In 1 Of 2 Accounts

System: Windows 7 Home Premium 64 bit

I previously posted something similar to this problem but have since discovered new information that places this problem in a much different light. Therefore I am starting a new thread.

I have two administrator accounts on my laptop - Admin_1 and Admin_2. With each account I plug in an external hard drive into the USB 2.0 socket. In account Admin_1, the drive shows up in Windows Explorer as drive letter E and I can access the drive in the Explorer right hand pane. But in account Admin_2, the drive does not show up in Windows Explorer. In account Admin_2, I can type "E:\" into the Windows Explorer address bar and then see the contents of the external drive in the Explorer right hand pane and can access the drive. So the only difference between the two accounts is that in Admin_2 the drive letter is not displayed in the left pane of Windows Explorer.

For both accounts, the items under Windows Explorer Tools ==> Folder Options ==> View are identical.

What can be different between the two accounts to account for this difference?