USB Flash Drive suddenly not appear as a drive

By the time you connect the USB Flash Drive (UFD) to your PC or laptop will detect it as a Removable Disk in "My Computer". However, the media reported that XP is not installed and can not be given a drive letter (drive letter).
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You think your PC USB Flash Drive (UFD) such as an external hard drive. Therefore,the need to ensure all the UFD has been compatible with standard hard drives. For that, open Disk Management Windows via “Start|Exploree” and right click “My Computer” to select “Manage”. Through “Strorage| Disk Management”, check whether the UFDis plugged been recognized as a formatted partition or just as a medium that has not been configured (unallocated media).

There is a possibility, you mistakenly delete a partition on the UFD or damaged partition table for a variety of factors. With the function "New Partition" through the media context menu, create a partition on the UFD. The assistant will do the formatting. If you want the file system or a specific cluster size, do it manually format.

easier ...
good luck ....