I have a 2017 12” MacBook. I tried to update to mac os Sierra and I lost WiFi connection in middle of the update and it messed up my MacBook and gave me the infamous question mark. I have tried to do recovery mode several times and every single time it updates I get the error message “An error occurred while preparing the installation. Try running this application again. My MacBook is bricked. What do I do? Should I download sierra to a flash drive or what do I do to get my MacBook up and running again?