Hello,
I am using Dell Latitude D620 laptop with Windows 8 on it. It was working fine. But, just from last week the CPU fan stopped running and the CPU gets overheated. I found one thing that the fan is working when I plugged in to the AC adapter. I went to a laptop repair shop and as they suggested I have replaced the motherboard with a new one but still the fan doesn't work.
If there is some problem with the motherboard as well then I don't need to return my new motherboard. Any help is very much appreciated.
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:Â 
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4. And then press the option highlighted in the last thumbnail:
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These are the best methods, and they will likely resolve your problem.
