This trick works in Windows XP, Windows Vista 32/64 bit and Windows 7 32/64 Bits.
Sometimes when you plug a USB device to your PC, although it is recognized by Windows (the safely remove device icon is present in the Notification Area), it does not appear in My Computer or Computer. It is impossible to access the content on the USB key.
Here's how to fix it.
Right click on My Computer or Computer then on Manage or in the Start menu, choose Run then in the new window, type the following command:
In the left part of the new window, click the Disk Management area.
In the right part, right click on your USB drive and select Explore from the menu.
Normally your key is now displayed in the My Computer Window.