Bug or just an overheat?

[Tiberius Fireskull]

Well, since last week or so, something has been happening with my computer. If I am playing pirates, after an hour or so, my computer shuts down. Just boom, without warning, shuts down. I've had this before, and I think its an overheat, but I'm skeptical. The fan on my computer is working fine, and the vents don't seem to be blocked. I am playing with my laptop on one of those stands, so the air can blow out freely without hitting the desk.

It probably is just something up with my computer, like something in the vents that I cant see, I just want to make sure that its not a bug in the game...

Little help plz?