but those aren't original batteries:

There is a difference in capacity between original and those “cheap” batteries. My original battery typically lasted 8 hours. My $10 ebay batteries (I bought 3) last only 6 hours.

Ignoring the ebay results and the one after them which is an obvious fake (Li-Ion), the next two do look like original, genuine Nokia BP-5Ls. In fact even buying one directly from Nokia isn't too expensive anymore apart from the disproportionate shipping charges.

Ah, well, I thought that you were referring to the first results. The rest aren't that cheap if the tablet itself is broken.

All, thanks for the replies! I tried the suggestion offered by vvaz but the N800 still won't turn on. I have no SD cards in the device at this time. Up until this problem happened, the battery was fine. It held a charge and powered the device for hours so it seems strange that it could go bad so quickly. I am left thinking that maybe the battery is totally discharged and the device is unable to charge it, for whatever reason. The next step, I suppose, is to buy another battery and/or charger and see what happens. Thanks again.

My unit was displaying the same symptoms, it was the battery.

I purchased a battery for the N800 on ebay and stuck it in the device. It powered up immediately and worked fine. However, the N800 won't charge the battery even though it indicates that it is charging. I left it "charge" all night and came back in the morning to find the same black screen that started off this misadventure. So, it appears that I have a bad charging circuit in my N800. Anyone have any idea how much this would cost to get Nokia to fix?