So the hardware is in your inventory but its not showing as active?
If so is your firewall set to allow the devices to communicate with the dashboard? You can get a list of required ports by going to the help menu in your dashboard and selecting firewall info.
If you have already done that have you tried accessing the devices local status page and manually configuring IP info.
It sounds like either the devices are not getting DHCP or your firewall is blocking its traffic. You could also try a factory reset.