reboot loop

Hi again!

After solving the last problem (PC won’t start), I still got one…
Now the computer goes through POST then a black screen and restarts.
I checked BIOS and it detects CPU, memory and hard disks correctly but not the DVD.
I try to boot without the DVD connected and still the same.
I don’t find the menu to try a safe mode start (F8 doesn’t work most of the tiime. When it works it takes me to another menu).
There is Win2k3 on the booting disc from another PC (worked fine).
MB: ASUS A8R-MVP
2 GB minne
Graphic: ATI all in wonder.

I check with the supplier and there’s no known issues with the graphic card and the MB

Any suggestion?