Hello benc555
It sounds like this is either one of our custom DCS servers or has been flashed with a non-Dell BIOS. I would suggest trying other common buttons for BIOS entry like Delete.
Enter the service tag here: http://www.dell.com/support/home/us/en/19?c=us&l=en&s=dhs If it cannot locate the system then it is probably not a C1100. Our DCS servers are commonly sold as their PowerEdge Cloud equivalent, but they are custom units built to the specifications of the purchasing company.
Thanks