USB flash memory stick problem

I was using my USB memory stick for the months without any problems. One day I just removed it from computer - of course, correctly releasing via removal icon - and kept for some hours not using it. Then I inserted it again to computer and could not locate it anymore. Computer wasn't restarted - just kept working all that time - memory stick wasn't used in anoter computer, nothing was installed or changed in the settings. Memory stick is perfectly working on another computers. Other memory sticks are also working perfectly with my computer.
An interesting moment is that when I insert memory stick into usb, computers gives sound as to be aware that some device was plugged to it. Memory stick flashes and lights on. Everything seems to be ok except for that I cannot see it, no drive letter is assigned to it.

I have tried to revival it without any success. What I can rule out as a cause for a moment is:
i) usb port is ok (working with another sticks)
ii) memory stick is ok (working on another computers, no data missing, read/write ok)
iii) should not be any problem with driver(s) - working before without problems
iv) the above three facts rule out any device comflicts

Does somebody have any idea what is going on ?

Thanks in advance !

nalim