Well, I'm not watson, but I've had the exact same problem on my latest render (wich I will upload later this evening). In my case my CPU got too hot. Normally the air in the room is about 20 degrees, but now with all the hot wather the temperature can rise to 40 degrees in my room, that means it's a lot harder to keep the CPU-temp down. With this hot weather my CPU is about 66 degrees celcius (about 150 F) when it's doing nothing and that's far to high, so I opened the side of my case and pointed a big fan at it. The resulting increased airflow solved the heat problem for me.

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