Well, here's something to try.
1) Get any flashlight app in the store that allows changing screen brightness.
Or you can get our free Mirror app.
In that app change the screen brightness to low. Something like 5%. Make sure you see where the controls are - otherwise when you darken the screen you won't be able to see.
Now your device isn't asleep. However, the screen is effectively off so power usage is very low.
Settings also allows changing screen brightness but not to the extent that some of the flashlight apps.
I've had the same problem. The first few times it happened to me I just figured that I had done it too quickly and not paid attention to see if it really had gone off. This is particularly frustrating when you are traveling somewhere and the battery goes dead because the unit didn't power off.
I had this problem shortly after I bought my nook tablet a little over a year ago but I didn't take it seriously because I keep my nook on all the time anyway. But when my nook freezes or whatever the case may be it sucks that I don't have the option to shut it off unless I let the battery go dead but I don't like doing that. I seriously think I got a faulty one but now it's not under warranty. I still would like to take it in to see if it's fixable.
furyss2, do neither of these work for you
Press and hold power button for 20 seconds.
Press and hold power button and 'n' button for 30 seconds