Thanks for you feedback rdave13. I've been struggling with this problem and tried numerous fixes. I've read on the Internet that USB problems can cause my shutdown/sleep problem. I fitted a USB3 card to drive my relatively new USB3 ext hd. I've been trying it with the hd on and off now for quite a few times, and so far it's been very consistent in working normally with the hd on and with shutdown problem with the hd off. I can live with that if it's proved to be the problem. I may remove the USB3 card and try the pc without it to see if it proves the point.
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