If you have reset your Dell 3000cn or Dell 3100cn printer back to the factory defaults by clearning the NVRAM you will find that the username and password used to authenticate the web admin tool has also been set to the factory default. The default username used by the Dell printers is admin and the default password is password. After logging in using the default password you should immediately change the password for admin so that your printer cannot be managed by unauthorized persons.
If you need to reset the password or other settings like network TCP/IP settings on your Dell 3000cn or Dell 3100cn color laser printer you can do so by clearing the NVRAM which sets the printer back to factory settings. Unlike many printers the Dell 3000 series of printer requires that you clear the NVRAM in two places. So if you want to reset the network settings and clear the password you need to clear the NVRAM in the Maintenance section of the menu and the NVRAM settings in the Network Settings menu. In my case I had found the Clear NVRAM option in the Maintenance section of the printer menu but it still required a password to change the TCP/IP settings and still held the old IP. Oddly when I went deeper in the menu under Network settings I found another clear NVRAM option and cleared that. Now the printer got a DHCP address and went back to the default admin and password password settings.