It depends on whether it occurs randomly or when carrying out specific functions; for example, the difference between the laptop freezing and restarting after a certain period (a couple of hours) of use or the computer freezing and restarting when attempting to run a specific application.

Based on the information you’ve given me, it does appear as though the laptop is overheating, this could be occurring because the CPU fan has died or because of dust build up within the interior of the laptop. However, of the two, dust build up is most likely the cause, this is because the laptop is able to detect fan failure and thus notify you of its occurrence.

For solutions, you could try purchasing a laptop cooler; they’re relatively cheap, installed underneath the laptop. Alternatively, you could try monitoring room temperate or have a fan blow on it (laptop); you could also try positioning the laptop on a book, which is a somewhat effective method of ventilating the laptop.