Where did it fail? Did it get past the initial firmware and see you USB drive? Did it fail at the color screen? Did it stop after giving you an initramfs prompt? We will need a bit more information to be able to help you out. Hey! Thanks for all info! The first time your guide worked for me. My Rpi...

I had a problem! My RPi worked for 4 days and then I had to turn it off and I could not turn it on. Then I did it all over again "dd if=vmlinuz bs=1 | zcat > vmlinux" in the "system-boot", replaced the .elf and .dat files, but USB boot failed. Can't you tell me where I was wrong?