|See response 2 !!|
Other than the causes at the link referred to in that....
- the USB port may be physically damaged - in that case NO USB device may be reconized when plugged into that part - try it in a DIFFERENT USB port.
- if you or anyone else have dropped the USB drive or have otherwise physically damaged it, the drive won't be recognized properly when plugged into ANY USB port on ANY computer.
- note that if the USB port wiring to a case port or a port in a slot space from the header on the mboard has the +5v and ground for that circuit backwards, a USB flash drive will be damaged instantly when plugged into that mis-wired port and will never work again
- some desktop mboards, e.g. many Asus models, have 9 pin headers for both two USB ports and a single firewire port that are identical. If you wire up one or two USB ports to the firewire header, or wire up a firewire port to a header for two USB ports, nothing happens until something is plugged into the mis-wired port, but whatever you plug into ir is damaged instantly and can never work again, and your mboard may be damaged in a short time