How to assign a letter to a USB device that has not automatically been assigned one
1. Insert the desired USB device into any free USB port.
2. Open START, right click on the MY COMPUTER icon and select MANAGE
3. On the left side of the window that open's you will see a list of icons left click on the DISK MANAGEMENT icon and on the right will appear a selection of disks attached to the computer I.e.. CD Rom and your Hard disk you should also find the name of your USB pen.
4. On the device "highlighted blue" right click and select CHANGE DRIVE LETTER AND PATH. you will be then presented wit a new window with your USB pen name and three tabs bellow select CHANGE now select a new letter I tend to go for letters above G as these are not normally used and select OK.
5. you will now be shown a conformation warning stating that if you change the drive letter the device might become unusable, click OK to accept the warning and now the device should show the device name and the letter you assigned, if you close all the boxed and open MY COMPUTER your device should now be ready to use.