KNOPPIX splash screen at boot freeze my machine

Hello,

I have problem, please help me.

KNOPPIX great software, and i use many cases:
New installs, backups, cloning. Generally KNOPPIX works well (90%>)

Problem:

I bought a new pc with new video card (Matrox G550 PCI Express 1x ) i have also a AGP version of this, works well in my old machine, but new motherboard only have pcie 16x and pcie 1x interfaces.
Problem description: if i try to boot KNOPPIX (or any graphical splash screen bootloader) my pc completely frozen, but if i insert a 16x board (ex. ati x300) to machine, KNOPPIX can boot, and works well. I absolutly confused. What did the splash screen with my card? I understand, the problem not in KNOPPIX i, but i don´t known what is the problem, and cannot make support request to matrox or my motherboard vendor.
The question: What do the splash sreen with my card, why freeze my pc why not freeze with other pcie card what is special in splash screen?
My card (PCIe Matrox G550) works good after boot (with not graphical bootmanager) works with xorg, xfree86, with properitary mga driver, mga_vid, matroxfb.

Thanks.