PC reboots at white screen @ installation

Hi, first my PC:
ASUS P6T Deluxe v2
18GB RAM
i7 920
nVidia GTX 470

I use the following way:
boot with "iboot" cd and then start installation from USB-Stick...

I take some seconds (usb stick is working) and i see a white screen (i think with apple logo) and instant reboot.

Options like -x procudes a black screen and nothing happens (after load of extensions) and -busratio=20 -cpus=1 show me the white screen but nothing happens :( (pc is idle at this state)

-v option is not usable, because the pc restarts directly.. any ideas ?