It can be a number of things, but often times it's the thermal cycle and wear on the components. After letting devices (especially that rarely do this) cool, a

It can be a number of things, but often times it's the thermal cycle and wear on the components. After letting devices (especially that rarely do this) cool, and then bringing them back up to temperature some percentage of components may fail or operate out of spec. And mechanical parts have similar issue. A motor that's been happily running for months/years may not restart after being stopped. It's also possible that a power fault itself could damage hardware, although in my experience this type of issue is far less common.