Seagate, who have taken over Maxtor, have an installation guide
here for Maxtor Network Drives.
I suggest you follow their instructions for resetting the drive after "moving to a new network" then format the disk in your required protocol and use it. As was said earlier we cannot provide help with passwords, even if we knew what password may have been used.
The previous owner of the NAS should be able to supply you username and password if it's critical.
I did exactly the same when my Sister donated an unused NAS to me.