I assume you are using a thumbdrive. you have not set the device as bootable. My admin used to ride people for less, when you post more verbosity.
sudo fdisk /dev/sdbX
Select "a" - Active - select active partition.
Select "w" - Write.
If you still have a problem I will address.
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Main O/S: Builder of O/S Guess.
Mainboard: ASUS Sabertooth 990FX TUF (The Ultimate Force) R2.0
CPU: AMD FX 8150 Bulldozer Eight Core Black Edition
Ram: 16 GB GSkill Ripjaws Dual Channel DDR3 2133
Video: 2 X ATI 7770HD GHZ Edition 1GB PCI 3.0 Crossfire (main cards) various others for testing
Hard Disks: Over 30 TB Mechanical and Multiple SSD's. (Sans Digital 32TB raid tower - dual Esata)
Raid: Onboard 10 sata / e-sata ports, HighPoint RocketRAID 640 PCI-Express 2.0 x4 SATA III (6.0Gb/s)
custom software mirrored - tmbackup
Monitors: 4K Samsung 28", HannsG HH281, Various others
730 Watt modular PSU
700 Watt Amp & 4 X 600 Watt speakers