Does your laptop shut down in the middle of doing something without any reason and warning? Does your laptop run much hotter then before, the keyboard and the bottom part of the laptop feels very hot? If yes, your laptop overheats and has to be cleaned up. It happens because the heat sink is clogged with dust and lint preventing normal air circulation.
These are all the symptoms of a laptop overheating problem in or around the cooling system. The fan and the heat sink have a small gap in between them, this is where dust will be sucked into and will accumulate. Once all the dust and lint is removed, re-assemble your machine. This procedure is something that should be done periodically to ensure that your laptop overheating issues will be a thing of the past.
Alternatively, you can clean up your laptop without taking it apart by blowing off fans and heatsink with compressed air. This is not the best way to fix the problem because some dust will stay inside the laptop but it will work. By the way, if you’ve been using your laptop for a few years, it might be a good idea to replace thermal compound on the processor. It will help to keep your laptop cooler.
Here’s another resource with covers laptop overheating in more depth.