2 
1 Blackscreen, no chime, fan on, motherboard led on
I recently fixed this iMac with a new SSD, installed Linux and everything was fine.
Suddenly it just doesn’t start anymore.
Fan is spinning, motherboard led is on, but that’s about it, nothing else happen.
I was able to get it on once after this behaviour, by just unplugging cables and plugging them back. But no more since.
I’ve tried SMC, NPRAM reset.
When I remove the RAM and turn it on, I’ve the “hardware beep” indicating hardware issue. When I put it back on, its back to the same issue
I take this as a good sign. It doesn’t feel as anything is broken really.
but I’m short of ideas on how to proceed further and try identifying what’s wrong.
Any tips?
Update (01/19/2022)
Well, as I was about to try T key, the iMac chimed and displayed a white screen that seemed to last forever.
After trying OPTION key and PRAM reset, to no avail, I tried SMC reset by just unplugging the power cord.
After trying PRAM reset again, I just got the linux installed OS to boot, after a quite long time thougfh, like 20-30s. But NO PRAM.
I’m not sure what’s going on but the entire thing is highly unstable. No sure what this is indicative of. Some dying hardware?
Ist dies eine gute Frage?
971 
Please review this Apple TN on the tone codes If your Mac beeps during startup let us know which one you have.
von Dan
It's really the RAM beep in my case, it occurs only when I remove the RAM (just to make sure it isn't the problem).
And it works as expected: does the RAM beep when the RAM is out, and back to "normal" when back in (i.e. nothing happens, only the fan starts)
von coolnodje