Mac shuts down during startup I'll be short and sweet. 

My hardware: 


Mid-2010 13" MacBook Pro 
P8800 2.66GHz Core2duo 
8GB aftermarket RAM
750GB aftermarket Seagate Momentus HDD @ 7200RPM


My software:


macOS Sierra Public Beta (latest version). 


The computer was feeling very sluggish last night, having trouble loading simple webpages (it spent 5mn on google.com) - so I force shut it down using the power button in order to start it back up (it sometimes goes a bit slow after a few days of uptime). 

When I booted it up again, it got stuck at 95% of the grey startup progress bar, and hung there. I restarted it again, and it started shutting down completely midway through the progress bar. 

What I've attempted so far in order to solve the issue: 


Command + Option + P + R to reset NVRAM - this never seems to have worked, as i was unable to make it restart the machine
Command + R to boot into recovery mode, which worked - First Aid failed with code 8, and the reinstall option was a no-go, because it stated my hard-drive was "locked". 
Command + S to boot into single-user command line - tried to run /sbin/fsck -fy, which failed returning disks02: I/O error


I get the feeling I've pretty much exhausted my options at this point. What I want to try again once I'm back home tonight: 


Command + Option + R to boot into internet recovery - I don't know how successful this will be given my "hard drive locked" issue
Try to get my hands on a USB boot drive/installer for macOS, and try booting and running Disk Utility once I'm booted from that. 


My own opinion is that it looks like my hard drive is shot. Do you guys agree? Did I miss anything in my troubleshooting process?

Also, since this lappy is my only macOS device, I am currently stumped as to how to get a bootable installer for Sierra. I only have access to Windows machines. Any advice on this front?

Also, if it turns out my drive is indeed fried, what are my options for recovering that which is still recoverable? 

Thanks a lot in advance!

-Karim
First Aid failing and a locked HD means your HD is failing. 

You should boot into internet recovery, and install OS X on an external HD. (Since you don't have another Mac). Then, boot from the external HD and backup any important files from your internal HD. I'd recommend getting a new HD or SSD and installing it into your machine.