mouse died during os upgrade, then computer froze. How can i unfreeze?

The following will require any USB keyboard and mouse. If you don’t have them, borrow or buy them, they are inexpensive!

·        

• Connect the USB keyboard and mouse to the computer.·        
• Open System Preferences – Bluetooth·        
• Un-pair the wireless keyboard and mouse.·        
• Turn off Bluetooth·        
• Restart the computer in Safe Mode per the directions in https://support.apple.com/en-us/HT201262·        
• Restart the computer normally.·        
• Open System Preferences – Bluetooth        
• Turn on Bluetooth·        
• Re-Pair the wireless keyboard and mouse.·        
• Unplug the USB keyboard and mouse and begin testing the wireless devices again.

Hold down the Power key until the computer shuts down completely.

Power up the Mac and see it it will continue with the upgrade.