Latest Mojave Update on my 2010 Mac Pro resulted in "no startup"

Uh Oh!

I have a 2010 Mac Pro with an upgrade to Mojave. It was running fine with the latest version of Mojave until yesterday when I received a message that an update was available. It was a two part update, one for Safari and one for the Operating System. I've installed these in the past without any problems.

The Mac has been upgraded with 96 Gb ram, new hard drives, and a new graphics card, which is a Radeon VII with 16 GB of ram.

I've been very pleased with the upgrade and have been running it this way for about a year without any problems. It's a workhorse for me and I do a lot of video editing in it. Nothing serious or professional; it's just a hobby for me.

Now, after installing the latest Mojave updates, the Mac will not start! When I press the startup button it lights up and I can hear the drives start to spin. I do not get a chime sound. Nothing appears on the computer's displays except that the display's LED lights light up indicating they are getting power.

All of the drive bays have drives in them. The startup drive is the only drive with an OS on it.

However, here's what I do have:

I have another Mac Pro 2010 that works, though I haven't started it up in over a year. It is running Mojave, but has not been updated.

So here is what I am wondering about. Is it possible for me to

• pull the startup drive from my mac that no longer starts up,

• put that non-working startup drive into one of the hard drive bays on my 2nd Mac Pro 2010

• just copy the Operating System to my workhorse Mac Pro 2010 startup drive

• take that drive and put it back into my workhorse Mac Pro ???

I think that would work and my workhorse mac pro would start up again, but I'm not an expert at this sort of thing, so any and all comments about this plan would be very much appreciated.

Thank you....