sandisk u3 cruzer micro usb device stopped playing ?

You might try plugging it back into your computer, and formatting it. If you don't know how to do that, pull up the screen right BEFORE you would open it to copy music to it, right click on the flash drive, and click format. Format it with whatever the default format is shown (probably FAT32) and then copy your music back onto it. It should work, let me know.