My creative zen mp3player isn't recognized by my pc..?

I got a Creative Zen mp3player but it quit working after a few days. I returned it and got another one of the same kind. The brochure instructed not to plug in the device until the software was installed. The software from the first product was still installed on my computer, so I charged it anyway. Now my computer won't recognize the device when it is plugged in. I tried unplugging and plugging it back in and restarting my computer to no avail. I even reinstalled the software. The device is still unrecognizable. What do I do?