Thanks Meter 688
Join Date: Jun 2013
Location: Porto Alegre,Rio Grande Do Sul,Brasil
bootloader its there , since its the one who starts the kernel/recovery,its more low level than kernel, it controls the buttons etc... .
for some reason its failing to boot into fastboot mode, try using adb reboot bootloader (looks weird to do, but on early nexus 7 2k12 bootloader there was some problems that doing this would do the trick, also do it while system is running or in recovery), if still goes black screen, re flash bootloader using dd comands in the recovery(there is a thread to fix no bootloader things, look at it)
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Nexus 4 / 16gb
Nexus 5 / D821 / 16gb / ? / ? / ?
New Nexus 7 wifi / 32gb - Android L Developer Preview
Galaxy S3 Intl(I9300) - LS KK 3.1 (4.4.4)