3 Crashed Macs within hours - Won't boot - Shuts down after logo

2 iMacs (running Yosemite and El Cap) and a MacBook Pro (Yosemite) do not boot.

I am recovering from a brain injury, so my mind is completely over taxed right now.

Backups (of the boot drive), don't remember. Maybe, but no clue as to where, if they exist. The majority of my other data is backed up across a ton of mirrored hard drives.

Each system had been running for a extended amount of time. I was using one (iMac 27" 5k) when it felt unstable, so I restarted it. It locked up on restart so I held the button. It started to reboot, gets to the apple logo, the bar that runs across makes it about 1/3 to 1/2 then it goes dead. Hit the button on the back, and the cycle repeats.

It will not boot into safe or recovery mode. It has a fusion drive that I had a similar problem with that came unstable a couple years ago.

I put it into target mode and brought it up as a hard drive on my MacBookPro. Ran disk utilities, but it showed everything was OK. All files are accessible.

Afterward I tried rebooting my laptop, and it now does the same thing, except I can boot it into recovery mode. And If I can figure out where and how I have done a backup of it in the last year, I will try a restore, but the backup probably was a Carbon Copy Clone on an extra drive somewhere.

Now I'm freaking out. I go to my third iMac (old 27 running Yosemite), on the same network. I see the Sophos AV shield has an X and a pop up says autoupdate can't reach server. I run a system scan. I realize I can check email, but my browsers cannot connect to the internet. I start to try and troubleshoot but my username and password no longer give me admin access. The users control panel now says I have a standard account and there is no admin account listed. The Sophos scan continued to run at about 85% done, the last I saw. The system eventually went to sleep and wouldn't wake a up. An attempt to boot the system saw the same problem. It won't boot past the logo, stops at about 1/3 of the status line.

All 3 systems were running Sophos AV autoupdated within 24 hours. I have a 4th MacBook (running Sierra ) that I just pulled out, scanned with Avast, no sophos, and I used it to scan the target disk of the 27" 5K with no problems reported. Disk Utilities hasn't found any issues.

I don't know if this is a virus, and attack, or an autoupdate gone wrong. Any thoughts on where to go from here?

I'm pulling files I may need off the iMac27" 5K to an external from the running laptop. Once I know these files are copied, I'll do the same with the other systems, then get a little more aggressive with them.

Any thoughts?