Mac partition corrupt and can't boot into Recovery Mode

I have a dual boot late 2013 iMac which i bought in November 2014.. A few months ago I was playing a video game on the Mac partition with the Mojave OS and suddenly the graphics got distorted and pixelated and the Mac froze.

Ever since then it won’t boot on the Mac partition. The Windows 10 partition works great but when I try to boot into the Mac partition the progress bar under the white Apple logo stops at about 70% and never progresses. The recovery partition appears to be corrupt, even when connected directly to my router it shows the globe icon spinning and does a 3 minute countdown but then goes into the White Mac logo with the progress bar that stops at 70%. It doesn’t present any recovery or Disk Utility options, just switches back to trying to boot into the Mac partition.

I am wondering if some of the video circuitry failed (among other things) as when I went to install the video game (Insurgency) on the Windows 10 partition after the Mac partition failure it gave a graphics hardware error message, which of course I can’t remember the details of the error. But it didn’t give that error message when I had installed Insurgency on the Windows 10 partition in the past, before the Mac partition failure.

And I can’t boot from my Time Machine external drive, it stops at the same 70% progress bar.

Any suggestions? I would back up my Windows partition and do a complete low-level format of the whole hard drive but I don’t know how I could do that without a recovery partition or bootable media.

thankyou