Another very good resource is the slideshow tutorial that comes with RSNetworx for DeviceNet. You can launch it from the Help menu or search the Rockwell Software/RSNetworxii/ directory for PPS files.
Since the 1756-DNB is displaying "No Rx" we know that 24 vdc has been applied and that there is simply no master/slave traffic on the network, which is normal for an unconfigured scanner.
As Matt pointed out, the scanlist is downloaded to the 1756-DNB in RSNetworx, not to the ControlLogix CPU itself.
Because you have described "seeing all the communication modules" but not being able to "go online with the DeviceNet", and because you have two very new modules (1756-L64 and 1756-DNB Series C) it sounds to me like you do not have the Electronic Data Sheet file for the 1756-DNB registered.
Without the proper EDS file, the 1756-DNB will still appear in a backplane browse of the ControlLogix rack. But there will be no "+" sign to the left of it, because RSLinx Classic doesn't have an EDS file to inform it that the 1756-DNB is a network bridge.
With the 1756-DNB/C, you can right-click on the module in the chassis browse of RSLinx/RSWho and select "upload EDS from module". You can also download the EDS file directly from the A-B website and use the RSLinx Classic Hardware Registration Tool to register it on your computer.
1756-DNB Series C FRN 10 EDS file:
http://www.ab.com/networks/eds/cgi-bin/detail.pl?file=DN/0001000C000E0A00.eds
DeviceNet is a lot like swimming. If you don't know anything, and there's nobody around to help you, you're going to splash around and not get much accomplished. Take a couple of lessons, and you'll get along fine.