Hi again jhumroo,
First, it's is best to just continue with followup posts in the same thread otherwise it becomes difficult if not impossible to figure out / troubleshoot a problem. Since you have the one drive you thought was bad, do you have the ability to connect it to another PC and run the diagnostic software or not? If you don't do you know someone who does have this ability. That will tell you if you have a bad or dying drive. The same process could be used on the drive still installed, but at this point to try and rediscover your NAS, you could download Dlink's storage utility for your 320 and run it. This will find your NAS and it's IP in most cases and allow you to login to it. If it remains "lost", try rebooting your router and / or NAS to see if it shows up. If all of that fails, it is beginning to look like you have a possible hardware issue with the 320. A hard reset is also a possible step, use the little "reset" hole on the back, while powered on, insert a toothpick or paper clip for about 10 seconds and then release it. If it reboots in a couple minutes and remains "visible" on your network, you will have to reconfigure your users and settings. Then continue to try and trouble shoot. Good luck