I recently bought a usb memory stick, and had to return it because it did not work on either of my computers. In a few days I exchanged it for the same type of stick, and tested it at the store. it worked, but when i took it home it didn't work. then i returned it and bought a totally different one. when i got home it worked on the computer, and another computer, but then it stopped working. I would like to know what is wrong and how to fix it.