USB Memory Stick

I have a memory stick which suddenly stopped working on my PC. It is detected as being present in the device manager and listed in Disk Mangement in the Administrative Tools. However it is not assigned a drive letter and attempts to give it one don't work.

Obviously it's not listed in my computer. However the stick does work in SOME other PC's but not others both Pro and Home

I've reformatted on another PC which does see the drive but when it's put back in the original is still not seen.

Any ideas would be very welcome

G