I had similar problem, and basically CPU goes into sleep mode. Sometimes doing what you do wakes it up, but most times it doesn’t. The only way I could get it to work again, is to leave it on and drain the battery till it powers off on its own, then plug the power back in and turn on. Unfortunately, due to the low power consumption this could take days.
However if you manage to wake the CPU up again, and boot up, and the screen goes black again this is usually a hardware problem with the screen somewhere.
