SOLVED IMac mid2010 can't log into recovery or safe mode

[Tks]

I guess it had to happen one day ...
I'm running High Sierra on imac 2010 27" i7 with SSD (the system) and 1TB HDD.

I originally had a kernel panic, so I unplugged all peripherals restarted in safe mode and followed apple forums advice, that is:
- trashed non apple software (with Apptrap so that all related files are also trashed).
- ran DiskUtility > First Aid: no problems with volumes and containers but when I get to disk, both SSD and HDD have a problem and can't be repaired there, so the UtilityDisk mentions to reboot in recovery mode to repair the disks.

I'm stuck at this stage. I can't login in recovery mode (whatever combination shift and ctrl and cmd + R). I can't log back in safe mode either, or in normal mode for that matter. I reset NVRAM/PRAM as well just in case.
I made sure everything is disconnected, I even tried with and without ethernet cable.

I do have the startup sound and the progress bar, but once complete (takes a full 2 minutes though), nothing happens.
I know something is happening inside because I let it run a few times for quite a while, and the top left of the Imac is heating up considerably and fans start after 5 to 10 minutes.

Before I open it (I only did twice in 14 years to clean the dust), has anyone got an idea about what else I can do?
Should I maybe change the disks? I've actually just ordered the Luna Display to try and use the imac as a screen.
Talk about bad luck!

 

[TonyAguila]

Do you have access to another keyboard and mouse or trackpad? The keyboard, especially, could be the one preventing you from going into Safe Mode or Recovery. Is the SSD connected internally or externally?

 

[Tks]

Do you have access to another keyboard and mouse or trackpad? The keyboard, especially, could be the one preventing you from going into Safe Mode or Recovery. Is the SSD connected internally or externally?

Yes I tried a USB keyboard, same result.
The SSD is the original one inside the imac. I took care never to put anything on the SSD apart from system and apps of course.
Everything else was on the HDD, and I also migrated that on an external drive once it showed signs of slowing down more than a year ago. I only have my itunes library on it now. iTunes was slow, but it worked.
I was about to format this disk when it stopped working altogether.

 

[Tks]

As a last resort, I created a bootable USB key, and for some reason, that time it worked and I could reinstall High Sierra.
I erased the HDD (with itunes library) then ran Disk Utility, which doesn't detect any issue on any of the two drives anymore, plus the fans haven't started so far, though it still is hot on the top left.
As I'll have to use it as a display mostly in the future, do you think it is a good idea to get rid of the clearly old HDD and the DVD drive to make space and prevent heating?

Thank you for your help.