It sounds to me like the Zen you got may have some sort of bug. The best bet is to try and exchange it at the store, or under warranty through Creative directly.
Hi guys. I bought a Zen 8gb 3 months ago to replace my old Zen Nano.
I'm really happy of my choice and I've never had problems with it since now.
Considered that buying a Zen 8gb with a SD card 8gb I saved > 50