I just wanted to post this in case anyone else was having this issue. I had a problem where the computer would not shut down - went to a black screen, but power light (blue) still on .. needed a power cycle to restart.
Apparently this is a not unknown windows 8.1 problem. The solution (currently) is to turn off "fast startup" in power options (still starts quickly anyway..).
Specifically I get this issue reproducibly (repeated tests) when I try to power down with a SD card inserted. USB memory makes no issue.
As far as I know it's a Win 8.1 issue. Hope this helps someone else.
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