Does the fan still spin when it does power on? The protective measure of the board is that when the chip is too hot it will still power on but only for a second, then it will turn off with a beeping sound. If you suspect that the chip is too hot you might want to measure the temp. One other thing you could do is to reseat the Heat Sink and Fan assembly and make sure there is ample thermal paste.
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Does the fan still spin when it does power on? The protective measure of the board is that when the chip is too hot it will still power on but only for a second, then it will turn off with a beeping sound. If you suspect that the chip is too hot you might want to measure the temp. One other thing you could do is to reseat the Heat Sink and Fan assembly and make sure there is ample thermal paste.