Typically, a domain controller backup becomes tombstoned at 60 days, or 180 days, depending on how the tombstone setting was configured. Since your DNS settings were AD integrated, you may be out of luck . If you tried to re-introduce this DC into the domain, it could really wreak havoc with the AD replication.
If all you need to do is check DNS settings, you could try restoring this server in a lab environment, with the BIOS clock set back to a date earlier than 60 days. If it works, erase the hard drive(s) afterward and reset the clock so that this box could be used to build anther server