iMac won't boot

Hi,

My iMac (from 2011 I think, running High Sierra) won't boot. It keeps getting stuck on the loading bar screen, with the bar filling itself really slowly and then nothing happening once it's full.

I encountered a similar issue just after the High Sierra update and managed to solve it by resetting the NVRAM (cmd+alt+P+R on start-up)... I tried that again and this time it haven't fixed anything. I also tried to restart on Safe Mode (holding shift), and to reset the SMC, without any succes.

Therewas only one time when the NVRAM reset seemed tout work, I accessed a screen asking me to choose from various options (reinstall MacOS, restore from a disk, etc). I then chose to boot from my regular Mac disk, everything seemed okay, I went and did a check of the internal disk with Disk Utility, which said everything was normal... I tried to turn my computer off and on again to check, and ended up in the same situation as before, my computer not booting, oh and also overheating a bit.

Is there something else I could try ? Would there be a point in trying the same things again (since it almost worked once) ?

Thank you for reading me, I wish you a pleasure d'Ay !

Nat