OSX Prohibited symbol on Boot (High Sierra Update Caused) ive been researching and fighting this for a couple days now.  I tried recovery boot, disk utility, repair etc.. nothing seems to fix this...

heres what happened..

this 'puter was just fine, nothing wrong, runs great,  use it for software dev.  I "stupidly" clicked on update for High Sierra and it upgraded to high sierra.  rebooted, came up but was running slow.  

A couple days later, a high sierra update showed up, so thinking it would fix my slowness i installed it...

Rebooted... Prohibit symbol.. rebooted...  rebooted .... prohibit symbol...


PRAM reset, SMC reset, rebooted...  same
recovery booted, loaded recovery fine, did Disk Utility, it says the drive is fine. rebooted... same
recovery again, use terminal i can see the files, they are there, i can browse in terminal..
did FSCK from terminal completes all is fine... rebooted... same
created a recovery thumbdrive with a working copy of high sierra on another mac, booted from that, tried to do reinstall OS, did its thing, rebooted... same...
Tried the gpt delete add, rebooted ..  same...
Ideas?


Here are some details

-bash-3.2# diskutil list
/dev/disk0 (internal, physical):
   #:                       TYPE NAME                    SIZE       IDENTIFIER
   0:      GUID_partition_scheme                        *750.2 GB   disk0
   1:                        EFI EFI                     209.7 MB   disk0s1
   2:          Apple_CoreStorage Macintosh HD            749.3 GB   disk0s2
   3:                 Apple_Boot Recovery HD             650.0 MB   disk0s3

/dev/disk1 (internal, virtual):
   #:                       TYPE NAME                    SIZE       IDENTIFIER
   0:                  Apple_HFS Macintosh HD           +748.9 GB   disk1
                                 Logical Volume on disk0s2
                                 3219E74D-E794-411D-836C-39FA507F94C5
                                 Unencrypted



-bash-3.2# diskutil cs list
CoreStorage logical volume groups (1 found)
|
+-- Logical Volume Group 9FEA1FA4-F17A-4760-BDDE-26720CDAF4C5
    =========================================================
    Name:         Macintosh HD
    Status:       Online
    Size:         749296615424 B (749.3 GB)
    Free Space:   0 B (0 B)
    |
    +- Logical Volume Family CBEDC035-AB5C-4683-BC47-755288A34DE2
        ----------------------------------------------------------
        Encryption Type:         None
        |
        +-> Logical Volume 3219E74D-E794-411D-836C-39FA507F94C5
            ---------------------------------------------------
            Disk:                  disk1
            Status:                Online
            Size (Total):          748944293888 B (748.9 GB)
            Revertible:            Yes (no decryption required)
            LV Name:               Macintosh HD
            Volume Name:           Macintosh HD
            Content Hint:          Apple_HFS
I had a similar issue with my MBP 2012 (SSD installed for the past 3 years or so), never had any problems until after a flight the other day.
Thought the X-Ray may have damaged the SSD so reinstalled etc. and nothing worked.  

Turned out my data cable for the HDD is damaged and needs to be replaced.
Currently got my SSD in a disk caddy and working fine.  

I also used an amazing tool called Stellar Data Recovery on my iMac to recover data on the SSD before formatting which really saved my bacon.