If it is shutting down sporadically when it's hot (been on a while), then it is not really an error more a safeguard. One of my laptops shuts down quite quickly if I use it in bed (sat on the duvet) as it doesn't get enough space for the air to circulate, but If I use by the window it never shuts down.
Cleaning a laptop internally is not that easy as to do it thoroughly you'd need to dismantle it. But it could be that a tiny particle of dust has gotten between the heatsink and the processor, which would cause it the processor to overheat and then it would shut the comp down, but it would do that consistently if that were the case.
Make sure it is well ventilated (raise it up at the back is good) and the grills that are for airflow are vacuumed out, and see if it gets better.