Could be a temperature sensor associated with the CPU chip is mis-interpreting the temperature and thinking the machine is too hot, and setting a status flag that is meant to put it in safe mode or power it down but has the effect of hanging it.
Have you defragmented the hard disk recently? Problems with bad sectors *shouldn't* set in before booting but who knows.
I'm just shooting in the dark here, but those are some thoughts apart from the excellent ones Ciddyguy already gave you.
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Could be a temperature sensor associated with the CPU chip is mis-interpreting the temperature and thinking the machine is too hot, and setting a status flag that is meant to put it in safe mode or power it down but has the effect of hanging it.
Have you defragmented the hard disk recently? Problems with bad sectors *shouldn't* set in before booting but who knows.
I'm just shooting in the dark here, but those are some thoughts apart from the excellent ones Ciddyguy already gave you.