The best answer is B. Fan speed and airflow through the heat sinks. The symptoms strongly indicate overheating: the computer works normally at first, slows down as heat builds up, then locks up and powers off to protect the CPU/GPU and motherboard. The Quentin Docter study guide states that a PC that works for a few minutes and then locks up is probably overheating because a heat sink or fan is not functioning properly, and the first troubleshooting step is to check all internal fans and ensure the heat sinks are properly attached. High-end gaming systems are especially heat-sensitive because CPUs and dedicated graphics cards generate substantial heat under load. The same section notes that CPUs are common overheating sources and video cards are also very susceptible in gaming or graphics-heavy systems. Power supply testing is useful for intermittent power problems, but the gradual slowdown before shutdown points more directly to thermal throttling and heat buildup than voltage failure.

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