Which windows operating system are you using, XP, 7. 8 10?
Do you know the DHCP range of your router?
Power off the NAS and then check that the drive is properly seated in place. If it is do the following.
Download Netscan by Softperfect https://www.softperfect.com/products/networkscanner/
Read the simple on line manual and then use it to find your DNS-320L on your network. Note down the IP address. This will give an IP address for the NAS even if there are problems with the drive.
Open Firefox browser and put http://(the IP address you noted down) and press enter. This should take you to the NAS login screen. Login using the defaults and you should be able to setup and format your single drive,
If you can log in but nor find the drive then you might have a problem with the NAS or the drive (we have seen brand new drives fail on first usage).
Let us know what you find as there are other tests that can be carried out but they depend on what you find.