Plug the cable and Nook HD into your pc. Does it charge? If so, the wall unit is bad. Buy a new B&N Nook HD/HD+ charger.
Your pc makes for a poor charger, since it doesn't provide the higher amperage for a fast charge. But overnight charge might keep you going until you replace the charger.
This happened to me under warranty (within 2 days after purchase) and B&N replaced the wall unit. Apparently, the wall unit is a separate service part available to customer service.
Ok, perhaps I need to give more details. While I thank you both for your advice these are the things I have done to try to correct this issue as my Nook is my 3 year old's video game system.
1. Reseated the charger cable in the Nook itself as well as in the charger hub (wall outlet) portion.
2. Attempted to charge via my computer's USB hub
3. Attempted to charge via various USB wall charger hubs
4. Attempted to charge via USB hub on my laptop power converter cord
The problem does not seem to lie with the cable or charger hub, the issue seems to lie in the Nook itself. It has had a "short" since the day I received it that didn't register to me as an issue. Basically if you moved it from your lap to the couch/arm of a chair, it would put itself into sleep mode, which of course could be corrected by pressing the home (n) button. Now, nothing I do will allow me to charge my Nook and I am really upset by this.
I realize it's a material possession, but its a material possession that hard earned money was spent on that I do not have just laying around to buy another one.
I can't even power it on enough to get vital information like a serial number.
Sorry the reseat-into-the-hub trick did not work.
You can get your serial number from the BN website, in the "your nook" section - it'll appear on mouseover once you're in "Manage my nook."
It may also be visible on the flap that you lift to insert a microsd card into the device.
You're still under warranty and so you should be able to return for a replacement without a problem.