I had a recovery job come in for a hardware encrypted USB key, when plugged into any USB port:
Device Not Recognized was the message.
This customer had flown to Grand Cayman and his encrypted data drive would not identify to let him get to his data.
In some cases salty air can corrode the contacts on USB devices, or pocket lint/trash can obscure the proper contact points on a flash drive from being readable.
You can take a standard Q-tip and crimp it down, pull off some of the cotton and push the stick back and forth to clean the USB contact points.
To do this the q-tip must be fairly tight fitting between the metal frame and the circuitboard on the end of the memory stick.
This quick cleaning kept him from having to have actual data recovery done on his device.
We then set him up a second device with truecrypt encryption and transferred all his documents onto that device in case the device in question failed.