I have a Dell Inspiron n5110 and, like the subject states, the fan stops working after booting up Windows 10.
I just noticed this lately, so I can't really pin point the cause, but, I believe that it's only recent since my laptop ran smoothly in the past (I was playing the Witcher with medium settings, I was rendering 3d models/scenes with thousands of polygons, etc.), but now, it overheats every time I play and then shuts down.
I already tried cleaning the fan, replacing the thermal paste on the CPU and the GPU.
The fan works when I ran Dell Diagnostics and when the system is POST-ing (upon start up), then when the Windows 10 logo appears, the fan stops. I already tried looking for a driver, but I think fans don't require drivers...?