If you own a router, I suggest attaching the DNS-345 to the router and using a reserved IP address through the router, with the DNS-345 in DHCP.
What browser are you using to access the web UI? The DNS-345 works best with IE and you may have some issues with other browser types. Although rare (this is something observed on some of the last generation NAS), it's possible the ShareCenter is confused by the Linux EXT partition created during your earlier failed formatting attempts. In cases like this, mounting the HDDs on a Windows PC, running a quick format as NTFS, and then deleting all the partitions usually fixes these types of issues.