Default No Os No Recovery & Boot failed

Guys, i need some help. i was messing with my nexus 7. then i tried to start fresh again by re-installing the stock 4.4.4. It's been a while since i flash Stock roms. So i find this tutorial, Erase boot, erase userdata etc. then when i tried to flash the bootloader, it always fail (unknown error). So im stuck with a OS-less Nexus 7 and no recovery. I can go to Fastboot. My device is recognizable through Fastboot devices. My old Rom was 4.4.4 stock. Please help me guys