> screen doesn't change to MOS output and stays at UBoot screen.
> I can hear the CD-Rom working, that means system has not crashed.
> I tried DVI and HDMI ports.. Any ideas ?

If this is on a Sam460ex and not on a Sam460cr, maybe MorphOS defaults to the VGA output of the on-board SM502 and must be switched to the PCIe graphics card after boot? Just a guess.