Hey there Carolynsd,
Thanks for posting and I'm sorry to hear about your Nest thermostat. I want to check on this further.
You’ll see the message you've provided if your thermostat doesn’t detect power to a wire, or it can’t detect the wires in your thermostat. Could you ensure that the power to your system is on? If they are, try switching them off then back on. If you still get the same message on your thermostat display, you might need to check on your thermostat wires. Take a look at this article on what to do next: https://bit.ly/3GuEdJJ
Keep me posted.