|Are you saying there are no other items in the boot order, or you can't change the first one? If there are other items in the list you may need to select an item and use the page up/ dn keys to move that item.|
Modern BIOSes also have two areas where selections are made. The first one is to choose between items like floppy drive, CD drive, hard drive, other bootable device.
The second is only to choose WHICH hard drive to choose as the first boot device. This is due to the multitude of SATA ports on modern motherboards. It is possible to have 6 or more bootable hard drives installed. So, make sure you are at the first list. Should be on the second or third screen.