Mac Unable to locate Start Up Disk after League Crashes

Hey everyone, I wanted to post this here to see if anyone else has been having the exact same issue as I have been having; I know some of you are having severe Mac crashes, but I'm wondering if anyone has had their mac crash to this extent.

I own an iMac [2012, yeah, she's old] with the latest Mac OS [Mojave] and a brand spanking new hard drive, that has been having issues with League for the past 5 months.

Sometime Pre-July [when I first downloaded Mojave and before getting a new hard drive installed], my League games would crash every other day, even the bug reports crashing to the point where I'd have to restart my computer.

In mid-July, my iMac crashed hard, but this time it would not start up at all -- the loading bar with the apple symbol would load about 20% before the computer would crash again, reboot, and start over, only to crash again and repeat.

So I went to get it repaired, cost me an arm and a leg of course ['cause it's mac], for them to determine that it was my hard drive that needed replacing [apparently]; thus I replaced the hard drive, thinking that this was the cause of most of the crashing and inability to start up.

At first everything was running fine, very fast and smooth, even League was running pretty well...but it started happening again. The game would, at first, crash once every week or so, but it's gotten progressively worse again to the point where it was crashing every other day.

In early-September, it crashed so hard during a League game, where once again it would not start up -- so I did my own factory reset, and managed to get the computer working smoothly again with no problems in the world...until once again, I redownloaded League.

History has, once again, repeated itself this October as my iMac crashed so hard last night that it can, once again, no longer start up...this time to the point like it had in July, where I am going to have to, once again, get it repaired and the Mac OS re-downloaded.

I am seriously beginning to think that the hard drive isn't the issue.

I know my computer is old, it's very old and will need replacement soon, but everything else runs fine on it. I can play other video games [Sims, Boarderlands, etc.] on it without it crashing, or having any problems, and all the programs and functions run smoothly.

The only time it crashes is when I am loading up or in the middle of playing League, and this is the third time that this computer has crashed during league and been unable to start up afterwards, to the point where I need to repair it for a second time.

This is why I have reached out to you all, to see if anyone has had the same, extreme situation as I have [with their computer no longer being able to start up].

I know some of you are having a very similar problem as I am, with it crashing constantly and even crashing their computer / machine, but what I am trying to figure out is whether or not it's crashing harder because my mac is old, or if people with newer macs are having the same crashing problem [to the point of not starting up and needing repairs].

Thank you all so much for reading my very lengthy explanation, and please let me know your thoughts or the mac crashing situations you've been having! Any constructive conversation would be greatly appreciated.