Your router should have a page for attached devices or DHCP leases or something similarly named.
Personally, I believe that all network shared resources - devices that are in some way shared, be they storage, printers, etc., - should have static addresses, set at the device, for ease of use, and the only reason I'm suggesting a reset to default for the original poster is that this is a new device and at this point unknown.
If you were using yours with a static address, then you'd have a reasonably good idea of where to look for it, and I would take a different troubleshooting approach - since you have reset it, you have no idea of where it will be, making that approach unuseable.
Is there a physical functional network connection to the DNS-323? What do the front panel lights show? The network link/activity LED is the bottom center - is it lit?