Are you running RAID? I've heard they cause a bit of trouble... Search the forums. I think people had to disable RAID, install, reconfigure something, then re-enable RAID.
It shouldn't be a BIOS problem... The normal setting for any computer is to check the MBR for a boot-loader. Unless you changed it and took the hard-drive out of the boot order. Did you tell GRUB/LILO to install on the MBR?
If you can boot from CD, then you should be able to use the install CD to get into the system until you figure the problem out.