ibm server boot

hello everyone,
1- i have ibm server bladecenter hs21 and i have problem with booting, my cd rom doesn’t work there is achoice boot from usb,network, and hdd, when i boot from usb cd rom no thing happen and tell me bios flash rom disable, why i can’t boot from usb cd rom please anyone help me with this problem

2- can anyone explain step by step the booting from network for ibm server bladecenter hs21 8853