My PC has started shutting down about half an hour into its use whenever I'm doing something processor intensive. If it's sitting, or I'm just on the internet, it's generally fine, but as soon as I fire up a game or something clunkier, it'll hang in there for a while and then conk out (shut down). I last had a similar problem several years ago when I added too many peripherals for my power supply, but that can't be the problem this time.
Due to circumstances, it's currently in a room and location where there isn't a lot of air circulation, and the air around it is generally pretty hot right after shutdown, so I suspect it's overheating.
Is there a free or built-in temperature monitor for/in Windows that I can use to confirm my diagnosis? I have a fan that I'll be installing to see if that helps - the old one's bearings are not in great shape.
If it is a temperature problem, is my only recourse at present to replace the case with one that supports more fans? What other options can I investigate?
Thanks in advance.