I'm sorry to hear that your Nest Hub is showing only black screen. A few questions: does it still respond to voice commands? When you change the volume, does it change? It would help a lot if you could do a sequential reboot first. Unplug the power cord of your router followed by your Nest Mini. Plug them back in after 3 minutes or 5 minutes tops. Restarting your phone might also help. If the issue persists, try other power outlets and hopefully it doesn't have a surge protector to it.
Thanks for the help, @RachelGomez123.
Keep us posted.