Good reply! Another question would be are you plugging the flash drive directly into a usb port or usb hub at all? One finding for flash drives when using a hub is using a hub that come with it's own ac adapter over those that power off the port only. With various brands even some will become fussy about how much current is available for them to draw on and will refuse to work. The self powered hubs offer a better regulated current.
A second thought would be trying it on a different port in case the port you have been using is giving out on you. This can happen over time from wear.