Help - Bluray playback - no video

[TehSofa]

I tried searching through the forum here and couldn't come up with any relevant solutions, so here goes...

The System:
OS: Windows Vista 64 bit
CPU: Intel Core 2 E6600 @ 2.4 ghz
RAM: 4 GB
Graphics card: Nvidia GeForce 7950 GX2
Gfx driver ver: 190.62 WHQL (newest)
Monitor: LG L204WT
Drive: LG GGW-H20L (Internal SATA Blue-Ray burner/HD-DVD)
Player software: PowerDVD 7.3.5105.0, TotalMedia Theatre 3.0.1.120
Test movies: Forbidden Kingdom and Watchmen, Bluray; multiple DVDs

(Personal build, not a branded box)

CyberLink BD Advisor gives a greenlight for everything. The monitor is OK'd on both analog and digital connections.

The problem:
Playback begins just fine in either player. After anywhere from a few seconds to about ten minutes, the video will just stop. The audio keeps going. If I try to seek to a different spot, the video output is all black but the audio seeks. The player interface still shows just fine, and there is no crash. If I close and restart the same player software, the video remains black. If I reboot, the problem resets. If I start the other player software, assuming I haven't already tried it since rebooting, it will work for a little bit and then stop working in the same way.

After it has decided Bluray shouldn't work any more, TotalMedia Theatre exhibits the same problem with DVDs. PowerDVD will still play DVDs successfully after screwing up with Bluray.

Both CPU cores still show a 30% - 50% load factor while playing the blankness, so clearly something is happening.

The only idea I can come up with at this point is that the 64 bit version of Vista was a bad idea. Can anyone give me some suggestions before I kill a day installing a different version of Windows?