Here we have a laptop that was brought in because it was crashing, assumption being that it was overheating.
We have examples of the front and back of the computer. As you can see, the exterior doesn't give much of a story. It's not particularly dirty, there is no obvious accumulation of dust buildup, etc.
However, it is very common for thick dust to build up inside of the heatsink against the fins of the exhaust. This creates the inability for the fan to do it's job properly because it can't get rid of the heat that the CPU/GPU produces through the build up.
This can result in the computer shutting itself down as a safety precaution or having permanent hardware damage.
There was dust buildup between the fan and heat spread. As you can see, there was a substantial blockage causing issues for the exhaust fan.
A nice, happy and clean heat spread after dust removal.