What browser (and version) are you using? IE and Firefox should work. Try clearing the browser cache and make sure everything is typed correctly.
If you performed a factory reset as you described (holding the reset button for > 8 seconds while the DNS-320 is powered up), then the DNS-320 should be accessible using the default user credentials on the web UI and your HDD configuration should be unaffected.
Is this how you performed the factory reset?
Also, what HDD configuration are you using?
