my iMac won't turn on at all

try this; unplug the power and press the iMac power button for 15 seconds. Before doing it disconnect all external devices. Then plug power back and try the iMac.

I had a similar experience since I owned iMac 10/2020.

We had a power outage since the snowstorm and my iMac would power up - black nothing.

Ready to go to the Apple store tomorrow and tried it again. It works.

Power + Command + R works for me the first time.

Control + Command + power works sometime.

I would try holding the power button long time to ensure the power OFF. then normal power on + comand + R

It happened to me many times.

VERY frustrating experience since Oct 2020.

I feel you. Hope this helps...

Can you elaborate on the "attack on the computer" please?