Did you specifically issue Shutdown? Or you are only closing the lid?
If only closing the lid, my HP has trouble waking up from hibernation (sleep is ok until it hibernates). I am confident the computer is running from the HDD activity blinker. But, no graphics. Probably a driver issue.
It's effectively "closing the lid". I had the problem again this morning so I tried pining the tablet from my other computer and got no response. I suspect this goes deeper than the display driver but that was a great idea. Thanks.