I recently had a similar problem with one of my DNS-325's. I use Raid 0 as I have multiple NAS's and they back each other up. First, one drive went missing, then the second disappeared. I tried several things pulled the power, let it set for a while, reboot, then I found the 325 could be found with the finder software, but when I tried to login, the login page came up, but nothing would load after that. Meanwhile I had been running the manufacturers diagnostic software on the drives and they were looking fine. Then tried the pin reset thing, still nothing but the drives were good, also swapped power supply, still no good. I concluded that the hardware of the NAS had failed.
Then I went to switching everything over to one of my backups, but the old one had been configured as an FTP server and had several more users and different permissions etc. as well as the Dlink DDNS stuff. Next step I thought I could use the configuration backup for the old FTP NAS to the new one. It took the config successfully, but the mismatch on the Device name resulted and I was unable to get into the GUI again. After a bit of pondering, I did a reset on the new one which allowed me login. Next, on a hunch, I changed the device name to the same as the old one which had failed and re-uploaded that configuration file again, this worked and allowed me to login. I then changed the 325's device name back again and bam I was good again, except for switching the FTP IP on the router and everything was back up and it was accessible from the internet.
The trick I wanted to pass on was about being able to use the config from one 325 on another one by switching the device name back and forth. Probably one in a million users might ever do this, but here is how.