This is because the Dell PowerEdge 1750 has bootsector protection which needs to be disabled in the BIOS by setting "OS Install Mode" to "On".
NB. Once you have successfully written your bootloader to the bootsector you must disable OS Install Mode in the BIOS or your will run into this problem www.chrisnewland.com/av/108/solved-dell-poweredge-1750-only-256mb-ram-available