PC fans running even though they are turned off?

Hello,

I've noticed recently that when I turn off my PC, the monitor turns off but the fans are still running and the AIO is still lit (NZXT Kraken).

Today, for example, when I turned off the PC, everything turned off except the NZXT AIO (water cooling), which still showed 25°, just like when the PC was turned on.

I then pressed the power button on the power supply and then the button on the PC case to turn off the power. I took a shower and quickly put my things away (about 20-30 minutes).

I come back: The water cooler still shows 25°C and is lit, even though I pressed the switch on the power supply. I then unplugged the power supply, and the water cooler immediately shut down.

After plugging it back in and then pressing the power button, the PC turned on immediately. Everything lit up again, and the AIO showed 25°C again, but there was no image (I waited about 10 minutes). When I pressed the button on the PC, it didn't turn off either. Even after holding it down for about 20 seconds, it didn't turn off, so I pressed the power button (the AIO was still lit, for whatever reason) and unplugged it.

Now my questions:

•Why is that?

•How do I fix this?

•How do I restart my PC safely without damaging anything?

Thank you very much for your answers and good night.