ASUS P4SDX AGP8X issue

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This week I bought a ASUS P4SDX motherboard which has a SiS 655 chipset which supports AGP8X. I also bought a PNY GeForce4 Ti4200 AGP8X card w/128MB memory. CPU is a P4 2.4Ghz. RAM is PC2700 CL=2.5 1GB memory.

The problem is that under Windows XP the display will "stutter" and parts of the graphics are corrupted. Also, the CPU will "hang" for a while and then pick up later as its talking to the graphics card.

If I change the AGP setting from 8X to 4X in the BIOS, the problem goes away.

I have tried the BIOS that came with the motherboard (v. 1002c) and also the latest BETA from the ASUS site (v. 1003 beta 006). I've installed the latest SiS AGP driver (v. 1.15) and the latest SiS IDE driver (v 2.03). I also have the latest nVidia driver (v. 4.3.4.5).

I've fiddled with a lot of the settings in the BIOS including:
- Graphics aperture size
- Video memory cache mode
- Delay Transaction
- Plug and Play OS
- PCI Latency Timer

None of these seem to have any effect.

I'd really like to use AGP8X since both the MB and video card support it.

Is this a problem with the motherboard's AGP slot or with the graphics card?

Thanks in advance for your replies.
--Anil

 

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One other thing that I'm wondering about is the power supply. It is an Antec 300W which are supposed to be reliable. The motherboard moniter states that the +12V supply=+11.247; the +5V=4.972; the +3.3V=3.184; and the Vcore=1.477. All of these seem a bit low to me. The system works very reliably in AGP4X, but not in AGP8X. Could this problem be at all be related to the power supply?