I have had something similar happen to my nook HD+. It seems these nook HD+ units have battery calibration issues, or the batteries aren’t very good. I would leave mine charging all day, then when I went to turn it on it was like it was frozen and wouldn’t do anything even though it should have had a full charge. Searching around the net I found that others have had this issue too.
To recalibrate the battery some said you can disconnect and reconnect the battery. I bought a tiny screwdriver to take off the back panel after prying off the plastic cover and bezel. Disconnecting and then reconnecting the battery did work but a few weeks later the problem returned. I don’t know; perhaps a new battery would help.
Strangely enough, I liked the HD+'s resolution but felt its performance still lagged at times. After two Nooks and a first gen Samsung tablet, I’ve decided, “no more tablets” for me. I get that they’re light and now have decent displays, but I need a real computer. Of course, even saying that I still use my original Nook Color on occasion. It’s portable and has proven more reliable than the HD+.
But now I use a 15 inch 2-in-1 laptop that converts to a tablet mode. Yes, it’s a bit unwieldy in tablet mode, but I mainly like using it for magazines and comics, which look great on that big screen.
Anyway, good luck with your Nook. Let us know if the B&N guys help you out or if they see it’s an older model and just laugh.