My iMac won't boot up!

Two days ago I was on the Mac and I turned it off. I then turned it back on like 30 seconds later and I don't know what my dad did but he tried to stop the computer from turning on or something or he was pressing the keyboard, because when I came back a while later, the loading bar on the boot up screen was frozen at 100%.

I then tried again yesterday to turn it on but it never booted up, it only froze on the loading screen. I even turned it on and left the house, and around 1 hour later, the computer was STILL frozen on the same screen at 100%.

So all day today, I was searching up the problem and tried everything I could to fix it, but nothing worked and it just seemed to get worse.

I was following this person's suggestions - My mac is stuck on the white startup screen!.

- Firstly, I think I tried to repair my disk through Disk Utility by holding (cmd+r) when booting up. It said it was done and it was fine. But when I restarted my computer, it still kept on freezing.

- I then tried resetting my NVRAM, but it still didn't work.

I then came across ANOTHER PROBLEM. I wasn't able to boot into Safe Mode... I held down shift after I heard the startup noise (I saw on a website that if you have a wireless mac keyboard, you have to press shift after the noise). I tried releasing it when I see the grey apple logo with the loading bar and I also tried holding it down until it would enter safe mode but I was just stuck there waiting forever. Neither worked. I was thinking the problem was that I'm not pressing the shift key at the right time or something like that.

- I THEN tried to go into single user mode and I typed /sbin/fsck -fy and it said my macintosh seems to be fine. Still wouldn't work... I searched up how to enter safe mode using terminal as I wanted to see if my timing pressing the shift key was the problem. I was going to enter (sudo nvram boot-args="-x") in single user mode and then enter (sudo nvram boot-args=" ") once I'm in safe mode to remove the setting. But then I got scared in case safe mode doesn't load like normal boot up and I wouldn't be able to do anything. I didn't want to mess everything up, so I left it. I also didn't know whether holding (cmd+s) would allow me to go into single user mode after I set the preset boot up thing to safe mode.

Later I then reset my NVRAM once or twice more and I tried repairing my disk, BUT SINCE THEN, IT HAS SAID NOTHING BUT 'FAILED TO REPAIR'. I even went to single user terminal and wrote /sbin/fsck -fy and fsck -fy again (think they're exactly the same) and it now says the volume has been edited.

I have also reset my SMC. Now whenever I turn on my mac, instead of getting stuck on the boot up screen, the loading bar goes to about 90% and then my computer just turns off.

I don't know if there's anything else to do now apart from purchasing an external hard-drive and making a new disk image of my mac and putting it onto the external hard-drive. And then factory resetting my mac and restoring from the disk image. I don't even know if this will work. Will it?

Could someone please help me. I'm begging you. I have my final GCSE exams (in England) in less than a month and I desperately need the computer working again. The last thing I would want to do is a full factory reset as I have family photos and important stuff on my computer.

Thank you in advance and sorry for the reaaallyy long question lol, I just want to go into as much detail as I can so it will be easier for you guys to help me.