Tried to update the OS on my MacBook and now it won't turn on!

Long story short...

I went to update my OS on my MacBook Pro and it froze at the last 5 seconds, after waiting an hour I did what I later learned was the wrong thing to do... Try to restart it.

Now when it turns on it's just a grey loading screen with the apple symbol, as soon as it finishes loading it then automatically turns off by itself.

I brought it to geek squad since I have insurance at best buy (got an open box deal, computer is only 1.5 years old) they kept it for a week and had no idea what to do, but suggested the hard drive was shot and to replace it... Before I do that, is there anything else I can try? Thank you in advance! I'm pretty desperate here

Yes!!!! For your ...is there anything else I can try????

Get it to a PROPER Apple Authorized Repair Tech and get it fixed for a problem that should have taken maybe an hour at most to diagnose!!!

Yes, I hate geek squad and plan on doing this... But I don't have a car and won't be able to get there for a few days so I was hoping I could try something in the meantime.

OK, but you might want to post some details of your MB model and OS X versions being used or attempted to update and use.

So if it's an old SL era MacBook, use the install DVD and try booting from it, usually holding the C key down when booting up.

For later OS X versions, try booting using the Command+R to boot from the Recovery HD, and then use Disk Utility to repair or fix your normal boot volume.

Have a look at Apple's kb article:
https://support.apple.com/en-us/HT201314

Hopefully that might be enough to get you back up and running.

Got a backup on an external hard drive by chance? Always do this before updating or upgrading.