Cooling fan not working properly

cooling fans that are ramping up to high rpm are doing their job typically. it may indicate that there are higher temps from either a high workload or just not properly cooling of components its there to cool down. when is the last time you serviced your laptop? dust/ debris, changing of thermal paste? id start there if the answer is over a couple of years. many tutorials to assist with this basic servicing, model independent. if you dont feel comfortable, a local repair shop can service relatively cheaply.

@wendeasrat Download the HP EliteBook 840 G4 service manual from under the Document heading on this page HP EliteBook 840 G4 Next, remove the bottom cover. Clean the inside of your computer with a brush and some Air-in-a- can. Check all the air inlets as well as the fan and the heatsink. All of those need to be clean. Given the age of your laptop and that is possibly already get's kin of hot, I' d suggest you re-apply new thermal paste as well. For that you will need to remove the fan/Heatsink assembly. Again , use your SM page 53 for instructions.

Since iFixit does not yet have a specific guides for this, use this generic one 放熱グリスの塗布方法 . The idea behind is is the same for your computer.

Now, I am sure you already have checked your software and checked the usage of the resources in Windows. Make sure you do not have any malware, spyware or any other software that drains your system resources through a high memory usage.