To nightbreed and Memonkey,
First try a different browser as suggested by JavaLawyer. The device should be accessible with or without a HD installed so...the first task is to determine if the router is assigning it an IP, you can try Ivan's suggestions, or just login to your router, somewhere there should be a list of DHCP devices with their assigned IP address. If available, copy down the IP address for your DNS 315 and enter it into your browser(S), try Firefox or Chrome if no luck in IE. If you cannot find the device IP, it might have been assigned a fixed/static IP outside the range of your router. The fix is a hard reset via the reset hole on the DNS 315, use a paperclip or toothpick and hold it in until the NAS starts to flash and then release it, give it a couple of minutes and then resume your search(s) for the device IP. Most hard drives are compatible with Dlink NAS's but to help insure the HD will be recognized, try first deleting all partitions and volumes then insert it as a bare / brand new drive. Good luck