tried everything and still can't get around prohibitory symbol. Any ideas would be appreciated. Desperate.

Excerpted from About the screens your Mac displays as it starts up:

Prohibitory symbol

A circle with a line or slash through it means that the selected startup disk contains a Mac operating system, but it's not a macOS that your Mac can use. You should reinstall macOS on that disk.

You need to try to boot into Internet Recovery by holding down cmd+option-r.

It will show a Globe instead of an Apple.

If you can get into that, you can use Disk Utility to check your disk. My guess is it has failed.

tried everything

What happened when you tried to Reinstall the OS in Recovery?

If that failed, when you erased the drive and reinstalled, what happened.

I remain desperate but also humbled by the people who showed their concern by addressing my problem. Thanks dot.com,Barney-14;E, babowa, and John Galt. I haven't gotten to all your referrals yet but I appreciate your time and will honor your effort. I confess I overstated by situation. Barney, I have note erased anything. I am not as knowledge as you all. I'm afraid of erasure. I will try to be more specific about problem. When I go into Recovery Mode, I get black field white apple. Progress bar goes only so far, then starts over I get another prohibitionary symbol. get another prohibitionary symbol: a circle with a slash across the middle, like a traffic sign. Like a railroad crossing signal, but with only one crossbar. Right now -- Saturday am -- on booting I get flashing question mark. I have a new ("used") macmini late 2012. I'm afraid I've gotten things out of order.. I know an reinstallation of system recommended, but I am unable to do that since I am unable to get to Recovery Mode. I'll let you know more after I have review reccomended research. Thanks for your efforts.

Thanks Barney-15E. I'm afraid you are right. I've already tried that key combination and it did not work. There is one thing I haven't tried (because I don't have the cable) is connecting my two mac minis with a fire wire cable. Thanks for hanging with me. I'll let you know the outcome.

Hey, Barney,

talked to apple support. said send it to the shop. I hate to give up. two things i haven''t tried. 1- connect two computer with a firewire 2- erase hard drive which i'm afraid of. I have two 8 T external hard drives. I would think you could connect them to the older mac and perhaps for the hard drive on one of them. but right now I'm getting a flashing question mark and the key combinations apple support gave me didn't help. I''ll let you know if there is any progress. Thanks all you fellows for pitching in.

Not sure what you mean -- maybe a screenshot showing the problem would help and what is the context, e.g. "in Pages I can't insert this symbol"??

Good luck...

Or are you referring to trying to boot up?