My Dell laptop CPU fan stopped working

My Dell laptop CPU fan stopped working

I see that there are a couple of reasons to why your CPU fan is not running as it should.

You said that the fan started running when you plugged your laptop in the AC adapter. I can figure out one thing from this: there might be a problem with the battery. How so? Well, usually a laptop fan should work within 12 Volts DC. If the battery does not provide a total of 12 Volts or a constant o 12 Volts, then the motherboard will take what it needs, leaving a number of components (like your CPU fan) , with no power input. When you plugged your AC adapter, that means it received the necesary voltage to start functioning.

Also, it might be a problem from a Windows profile. There is a slight possibility that a power profile has been changed, and CPU fan has been disabled while using the laptop's battery.

Here is what i recommend for this situation, and it's completely safe:

1. Go to Start and select Control Panel

2. From the Control Panel, select Power Options, like in the image below:

3. From there you will have to select one of the power plans shown in the image below: 

4. And then press the option highlighted in the last thumbnail:

These are the best methods, and they will likely resolve your problem.