scrambled video playing DVD in Media Center

I just built a new system using the Sony BDU-X10S blu-ray player. Blu-Ray plays fine using the PowerDVD Ultra software. However, if I try to play a plain DVD using PowerDVD Ultra or Windows Media Player, I get a message that my resolution needs to be lower in order to play the DVD due to copy protection (PowerDVD Ultra), or just that my resolution needs to be lower (Windows Media). If I try to play the DVD in Media Center, when the DVD starts playing, I get totally scrambled lines as if the refresh rate is incorrect (which I suspect it is).

I can set the resolution to 1980x1080 and down to 1024x768, but no lower. I can set it to 1080i, but not 768p.

This PC is hooked up to a Philips 1080i CRT television using the RGB outputs from an nVidia 8600GTS 512MB card.

Any ideas on how I can get the DVD to work? I had it working for a brief 10 minutes using Media Center when I first started, but I've obviously botched something up.

There are no problems playing downloaded video, internet TV, or HDTV via PCI tuner

Any suggestions?

MT

System:
Asus A8N-SLI
Athlon X2 4600+
2GB
EVGA e-Geforce 8600GTS 512MB PCI-e - HDCP enabled
HDTV Tuner card