Cannot access retail DVD media in Vista Ultimate x64.

I formatted my computer and installed Vista Ultimate x64. I have a HTPC case. It would be nice to use the Windows Media Center functionality of it along with my MS Wireless Entertainment Desktop 7000.

The problem: I can read any CD, and any burnt DVD. But, I cannot access retail DVDs such as Oblivian, F.E.A.R., Half-Life 2.

Windows simply does not acknowledge that there is media in the drive. I try to open (explore) the drive but it will not open. I don't even get an error message or anything. When I click properties on the drive, it says there is 0 bytes of data with 0 bytes of free space... which is impossible because they are game DVDs. There IS data on them.

The other thing I notice is that when I put in a disc that I can access (any CD or burnt DVDs), I notice the drive spins up like normal (the infamous whirring sound). When I put in a retail DVD, I can hear some faint sounds, but it doesn't do the high-speed spin up.

The drive is a Plextor PX-755SA. I've tried re-flashing the firmware to 1.08, downgrading to 1.07 (as per Plextor's "Vista compatibility matrix"), and even downgrading to 1.04 to no avail. It is currently back to 1.08 now.  I've tried re-mapping the drive to different letters. Still no luck with retail DVDs.

Also, when installing, I obtained ALL drivers for all of my hardware directly from the manufacturer's websites.  The BIOS on the motherboard is the latest version - 2101.

In Device Manager, I've tried removing, uninstalling, disabling, reinstalling, and update driver-ing (with many a reboot) and failed.

A couple other things I've tried:
- Many different BIOS settings including defaults. Fail.
- Disabling all non-Microsoft services at startup and rebooting. Fail.
- Seeing wmplayer.exe was a running process, I ended it and tried again. Fail.

I decided to try to access the drive with the tray open using the command prompt. Naturally, I got a 'Device not ready.' error. Then, I put in the F.E.A.R. DVD, waited about 60 sec. to make sure that it had plenty of time to recognize the media, and tried again. This time, I got an I/O error. (See code attachment.)

I've exhausted every idea I can think of.

1:
2:
3:
4:
5:
6:
7:
8:
9:
10:

Microsoft Windows [Version 6.0.6001]
Copyright (c) 2006 Microsoft Corporation.  All rights reserved.
 
C:\>d:
The device is not ready.
 
C:\>d:
The request could not be performed because of an I/O device error.
 
C:\>