save it for a day when you have motivation. the important thing is not to damage it more 😀 it only gets more valuable with time.

maxtherabbit is right. You need to stop trying to use the hard drive and focus on getting the 3.5" working as "A" drive.
If the computer sat too long the PSU, HD and floppies could be bad, capacitors fail quicker when not used for a long time (including those inside floppy drives).
If it were me I would: 1> double check the volts on all PSU leads at the mobo connection 2> pull HD cable and try just the 3.5" drive, make sure 3.5" floppy is at twisted end. 3> temporarily change CPU clock to 33Mhz.
4> boot from a known good floppy disk.... just thinking out loud ;p

I already removed the HDD, it’s in a K6-233 PC and works just fine. No alarming noises, no bad sectors.
The floppy drive is also working because I tested it in another system.
Something was different though: no post anymore.
Now there’s the video card line then, after like 5 or 6 seconds: FDD failure.
I also noticed that there’s no cpu message, but that might be normal for this bios.

Treat all isa slots with contact cleaner.
Does it boot when all HDDs and FDDs are set to none?
Edit : I forgot to ask the obvious: are you sure that ram sticks are all good?

Already spayed the slots with contact cleaner. And if I boot the system without drives I just see WAIT…..after the memory test.
(20096kb OK) so I assumed the RAM is really ok 😊

After switching the system on and off a few times the MHz display in the case suddenly stopped working. This pc is crap

At least I got it to post, after FDD controller failure.

Reduce ram to 4mb placed in slot 0. Does problem persists then?

Kouwes wrote on 2022-10-09, 14:07:

At least I got it to post, after FDD controller failure.

Serial ports 9FE and 375 ?
something screwy is going on.

Yeah I noticed that too, I enabled COM1 to 3F8 on the card. And disabled the parallel port but it still shows up.
Also, the first line of the border of the system configuration isn’t correct.

Have you tried swapping your memory banks around, or with just one bank filled ?
I can't recall if you already tried this and am a bit too tired atm to check.