Macbook Air stuck at startup screen

I have a Macbook Air early 2015 model. Three days ago I tried installing OS High Sierra. My Macbook crashed and I have tried all avenues to resuscitate it. I have booted in safe mode, recovery mode, verbose mode and single user mode but it won't budge. I have been stuck on the startup screen with the apple logo and progress bar at 100% for the past 3 days. I am unable to go to an apple support center because of the distance. What do I do to get it back up and running?