How can I fix this problem

Hello, KeithOfford.

That usually means that the startup disk cannot be found; it's offline or failed.

Please tell us about your Mac.

Can you tell us the model and year of your Mac and the version of macOS it should be running?

Can you start the Mac in Recovery mode while holding the ⌘R keys? From there you can perhaps use Disk Utility to run First Aid on the internal drive.

Optionally, maybe you have a bootable external drive you can plug into your Mac to boot from?