OSX Prohibited symbol on Boot (High Sierra Update Caused)
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.