Electronics naturally attract dust, debris and pet dander. After some time, if not properly maintained, dust can infiltrate your PC's cooling system - acting like insulation that traps heat inside instead of exhausting it out.
Some symptoms of overheating are sudden system shutdowns, fan error on boot, dirty components, burning smell, slowness or freezing.
Additionally, your system uses thermal compound to dissipate heat away from the CPU to the heatsink. After time, the thermal compound can deteriorate leading to insufficient heat transfer causing damage to your components
