Video/audio locks up when playing DVD or web-based video feed

This is a brand new system, just built from scratch.

Spec:
Motherboard – ASUS P5N-T Deluxe LGA 775 with Nvidia 780i chipset and on board RAID controller, Audio, LAN [LAN not used]
Graphics card – ASUS EN 9600GT silent, 512Mb, 256 bit - silent means it is passively cooled
2xWestern Digital Caviar 750GB 7200 rpm eSATA in RAID 1 [mirroring] config
Intel Core 2 Quad Q6600 2.4GHz
Kingston HyperX 4GB DDR2 1066
Sony Optiarc BC-5100S - 5x BD-ROM &12x DVD Burner SATA
Linksys wireless-N PCI adapter
Microsoft wireless, Bluetooth mouse and keyboard.
Windows VISTA 64 with service pack 1 and all new upgrades/patches
650W PSU

I installed new BIOS on the MoBo, all new drivers for MoBo parts inc audio, LAN, RAID and Graphics card, for wireless adapter and Sony Optiarc doesn’t have drivers because its an ATAPI device… but I did update the firmware to latest.

Cyberlink PowerDVD 9 Ultra - because I have the blueray and this is one of the few players available, the BD-ROM didn’t come with one.

So we are watching a DVD and all of a sudden, after 10 mins of playback, it locks up, the picture freezes, the sound [which is coming off the soundcard not through the HDMI connection] is clicking like the DVD is stuck and the only way out is to switch off power. I restart, resume playback and 10 mins later it does same again. – bad BD-ROM player or the Cyberlink software are my prime candidates…
Then we are watching a Netflix, instant view movie, and after an hour or so I get the same behavior even down to the sound which is reminiscent of a stuck record.

It seems to run cool when I have looked [32C for cpu and 34C for memory] My Graphics board runs at around 64C… which is about ½ way up their scale on their utility on which it is also listed as OK when I look.

Only 'overclocking' is that I had to manually set the voltage and FSB speed on the memory to the recommended levels, it defaulted to 800MHz and 1.8v.

Any ideas on where I should look for the problem? Things to try also welcome…

I was going to give memtest a go this evening and also get something to monitor temps. I should probably also see if there is anything in system logs.

It passed memtest. I still don't see anything in system logs and temperatures seem fine. Anyone know of a utility that will beat up on my graphics card and/or soundcard? - THX

Thanks - John