Laptop fan doesn't turn on after cleaning?

I just cleaned my laptop fan and replaced the thermal paste. Starting it worked without any problems, but when it seemed suspiciously quiet to me I noticed that the fans weren't turning.

My question: What could I have done wrong or where could the mistake be?

Fan cable not connected, loose, …

Either the CPU is so cool due to the new paste that the fan remains off for the time being. Or the cable from the fan was not reattached. OR the fan has been damaged.

I also bought replacement fans that don't work either. Does this perhaps point to another defect?