1080p stopped working on my HTPC

I'm having issues with my HTPC. Last night I installed a new internal Blu-Ray drive. Neither the hardware or software gave me any problems. I watched "The Fifth Element" in full 1080p without any issues, and it looked and sounded perfect.

Today, I picked up the new Indiana Jones movie, but it wouldn't play in 1080p. It looked like it was being played in analog, standard definition. Thinking this was a problem with the movie, I upgraded the PowerDVD 7.3 software that came with the drive to PowerDVD 8 Ultra. It didn't help. As a test, I put "The Fifth Element" back in, and now it's doing the same thing. Nothing was changed as far as the settings go between last night and today.

Here's the specs:

Asus M2A-VM motherboard
Athlon64 X2 4200
2.5 GB RAM
MSI GeForce 9400GT PCIex video card, w/512 MB RAM (with HDMI)
SB Audigy 2 ZS sound card
Windows XP Service Pack 3
Lite-on DH-401S Blu-Ray ROM drive

The PC is connected through HDMI to my LG 42" LCD (which does 1080p).

Any help would be appreciated - I've been at this for a few hours, and can't seem to find any answers.

At the moment, I'm not having any trouble outputting 1080p (it's 1080p60). I'm using the latest reference drivers from nVidia's website. Also, I just re-installed Windows and all the updates, with clean installs of all necessary driver. Still no luck.

Is there a chance this is HDCP-related? The BD Advisor from CyberLink says everything's okay with regard to my TV and hardware, but maybe it's not putting out 1080p for security reasons?

The display is 1080p, but the movies themselves appear to be only half-resolution. I can't figure it out. Like I said, 5th Element played perfectly, looked just like it did through the PS3. Then, overnight, it just stopped.

Some more testing reveals that I seem to have a very nice picture for about the first 3-5 seconds of the disc (the very first part of the Paramount title sequence, for example). At that point, the picture very clearly degrades, and doesn't come back.

HDMI doesn't work, neither does DVI -> HDMI cable. Audio is perfect; PowerDVD is remixing to AC3 and I have 5.1 at my reciever (an older Kenwood). So I'm at a loss here.

Yes, no change. Still looks crappy.

And I am running the audio through my HDMI, through the TV, and into the reciever.

Yeah, everything's fine, including playing games and watching video I have on my PC. The first time I played "5th Element", everything was working great. I have absolutely no idea what happened.

To answer your other questions, DVDs play fine, better than in MPClassic, in fact. And I've tried every setting in PowerDVD that I could get to, but nothign solved my problem (the settings had an effect, but it's still not as good as it should be).

With things as they are, the Blu-Ray "5th element" looks worse on my system than the Superbit DVD version. That really sucks. If this isn't an HDCP or a hardware problem, could it be a codec problem?

CPU hovers around 20%. Both movies use MPEG4/AVC1. I plan on picking up a stack of Blu-Ray discs from my brother and testing all of them. In the meantime, Cyberlink has suggested that I upgrade my video card drivers (which I've already done) and download the latest update for PowerDVD (which I've also done). Neither has worked.

I'll give that a shot. I'll admit, my dealings with Cyberlink have not been satisfying, but when the software was working, it worked very well.

I've written back to Cyberlink asking for a more specific answer to my problem; we'll see how that goes.

Okay, I uninstalled PowerDVD and, on a hunch, uninstalled and removed my sound card (the audigy 2 zs). I then reinstalled the old version of PowerDVD and fired up "Indy". The movie played perfectly (except with no sound). So I re-installed the sound card and tried it again - and the problem came back. I think swapping out that card for another will probably solve my problem (aside from the fact I already upgraded to PowerDVD8, but maybe that'll work now, too).

Thanks to everyone for your help. It's very much appreciated.