Are you running Windows? Does the player show up in device manager?
Try:
1. Find the device in device manager. Right click on it and select "uninstall device." Disconnect the device, and plug it back in. See if Windows finds it.
2. Try step #1, but reboot the computer before plugging the device back in.
3. Go into Computer Management --> Disk Management (or Drive Management, I can never remember). See if the device is listed there, and if so, what drive letter is assigned. It may be that Windows is trying to assign the device a drive letter that is already used by something else. Use Disk Management to change it to an unused letter.