osx 10.11 won't boot

Hello,

I just installed OS X 10.11 El Capitan on my computer from the app store and everything seemed to be working properly. Today, my computer crashed and restarted and it was stuck on the gray screen with the loading bar making no progress at all. I can't boot into the safe mode but have been able to access the recovery mode. I checked the disk utility and I see that my "Macintosh HD" is not bootable. I don't know if that's the reason or not and I don't know how to make it bootable from it. Please let me know if you need anything else from me to help solve this problem.

Thanks.