Prohibitory sign on start up


system: 24 inch imac (mid-2007) ma878ll

current configuration: system has been working beautifully last 6 months since upgraded hdd 1tb ssd , installed 6gb ram. have enabled trim on ssd , system has been working better did when bought it.

what has changed: when installing latest os x yosemite v10.10.5 , security update 2015-006, upon reboot system started load after 20 seconds of progress displays prohibitory symbol. when starting in verbose mode system hangs @ “still waiting root device”. also, system no longer has chime on startup.

steps taken far restore system: attempted following startup options directly connected keyboard , results follow each option:

start in safe mode – went straight prohibitory symbol.

start startup manager – went straight prohibitory symbol.

start bootable cd or usb thumb drive– went straight prohibitory symbol cd , usb drive.

start apple diagnostics – went straight prohibitory symbol.

start os x recovery – went straight prohibitory symbol.

start os x recovery usb drive in option mode– when booting option key shows primary ssd , usb drive. tried booting both end in prohibitory symbol.

reset nvram – went straight prohibitory symbol, although time startup chime came , has been working every reboot since reset.

reset smc - no effect, went straight prohibitory symbol.

start in single-user mode – went straight prohibitory symbol , displays “still waiting root device”.

start in target disk mode using firewire – works , able access ssd macbook. created image backup of ssd drive. ran diagnostics on drive disk utility revealed drive in perfect condition.

start in verbose mode – went straight prohibitory symbol after hanging @ osx kernel debugger, displays “still waiting root device” , repeats every 60 seconds.

firmware restoration – suspecting firmware issue, created firmware restoration disk macbook , followed steps apple support page install. according apple, directed hold power button until hear 3 beeps continuously, insert firmware restoration cd. when hold down power button 1 long beep , tries start up, ending in prohibitory symbol , doesn’t try read firmware restoration cd.

last operation made replace logic board battery , repeating nvram reset along rest of mentioned startup options resulted in same results identified.

understand system 8 years old has been working feel need @ least try keep alive longer. thing have not tried reinstalling os scratch, if can’t boot recovery mode or cd/usb, find impossible step. suspect hardware issue may preventing further progress wanted @ least put out larger community on issue.
 

how did enable trim on earlier version of yosemite? or, os did update from. did use trimforce command in yosemite? or trim enabler, turned off kext signing, , modified kernel extension? if latter, use instructions site "undo" modified kernel , turn kext signing on..

https://www.cindori.org/trim-enabler-and-yosemite/
 


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