So, in short it doesn't output enough wattage when cold or left for a year or two. What I recommend: if it's the full tower, replace the PSU to higher wattage (should just be ATX), meanwhile other ones are usable when you aren't pulling too much current.
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Edit: I tracked down what form factor of PSU I have. It's TFX, which is very office computer (HP, Dell and even some servers)
So, in short it doesn't output enough wattage when cold or left for a year or two. What I recommend: if it's the full tower, replace the PSU to higher wattage (should just be ATX), meanwhile other ones are usable when you aren't pulling too much current.