Question Back and Front Fan not spinning

BasicConcept

Honorable
Dec 29, 2019
110
3
10,585
My PC is 3 years old and I did not built it myself. I also do not remember if they ever were spinning but judging they have loads of dust on it and the thin layer that holds that dust is dirty, I think it was always spinning.

Today I installed a new RAM. Took out the old RAM, put that new RAM in and just attached the fan in the middle of the hardware back. I use the Bequiet silent wing 3. After putting everything back without touching any cables, I see the back and front fans on the PC aren't spinning.

Perhaps it regulates its temperature by itself and actives if it gets really hot? I am doing mathematical solving on my PC where the CPU is at 100% so I want to make sure it cools properly.

What could be the issue? Or is it normal?