Fan
The fan that you can see on the back of the computer is not a connection, but it is critical to the health of your computer.
It cools the power supply.
There is at least one other fan inside the computer, which keeps air flowing inside the case to remove the heat that all this processing generates. If things get too hot inside the casing, the CPU will fail to calculate accurately. You will get wrong answers, the wrong commands will be executed, there may be unpredictable crashes of your programs. This could be annoying or disastrous, depending on exactly what happens. If you have trouble only after the computer has been on for awhile, you can put HEAT on the top of your list of suspects.
Never block
the vent holes in your computer's case. Blow the dust off the blades from time to time.
Noise: When your computer first starts up, most of the noise you hear
comes from the fans.
If you ever fail to hear
a fan running, don't operate the computer until it is fixed or you'll be risking serious damage from heat.