My iMac boots to a circle with a slash in it. It won't boot up.

I am using an iMac 27 Quad iCore 7 running macOS 10.15.7 which is as high as it can go. I disconnected all of the peripherals except for the keyboard. I tried reseting the pram with Shift-Command-P-R. No luck. The apple and loading bar comes on to about half way and then it stops. I will include a picture of the screen at this point to show what happens.

Thanks for any help you can offer.