First off I would verify that the disk actually works in something. Either a standalone DVD player or another computer, it doesn't matter just something.
Next I would attempt to rip it off the disk using Mac the Ripper. Try different regional settings.
If you can't find anything else that will play it, and you can't rip it, the disks themselves might be bad.
Standalone DVD players
Usually a configuration flag is set in each player's firmware at the
factory. This flag holds the region
number that the machine is allowed to
play. Region-free players are DVD
players shipped without the ability to
enforce regional lockout (usually by
means of a chip that ignores any
region coding), or without this flag
set.
However, if the player is not
region-free, it can often be unlocked
with an unlock code entered via the
remote control. This code simply
allows the user to change the
factory-set configuration flag to
another region, or to the special
region "0". Once unlocked this way,
the DVD player allows the owner to
watch DVDs from any region. Many
websites exist on the Internet
offering these codes, often known
informally as hacks. Many websites
provide instructions for different
models of standalone DVD players, to
hack, and their factory codes.
Computer DVD drives
Older DVD drives use RPC-1 ("Regional Playback Control")
firmware, which means the drive allows
DVDs from any region to play. Newer
drives use RPC-2 firmware, which
enforces the DVD region coding at the
hardware level. These drives can often
be reflashed or hacked with RPC-1
firmware, effectively making the drive
region-free. However, this usually
voids the warranty.
In most computer drives, users are
allowed to change the region code
(i.e. change region code) up to five
times. However, if the number of
allowances reaches zero, the region
last used will be permanent even if
the drive is transferred to another
computer. This limit is built into the
drive's controller software, called
firmware. Resetting the firmware count
can be done with first- or third-part
software tools, or by reflashing (see
above) to RPC-1 firmware
Software DVD players
Most freeware and open source DVD players, such as VLC, ignore region
coding. Most commercial players are
locked to a region code, but can be
easily changed with software.
Other software, known as DVD region
killers, transparently remove (or
hide) the DVD region code from the
software player. Some can also work
around locked RPC-2 firmware.
From Wikipedia article on Region Codes