OK so I do not own an N8x0 but the above screams to me, "bad battery!" Espetially given the background, the device being not used for a long time (years?).

The battery may not be charging at all. The device starts, drains whatever little juice is there left, and reboots. If the battery is really bad, it may never charge. I would start by trying to charge it externally (out of the phone, with an external charger if you have one), to confirm it boots at all. If I am right, the battery won't hold the charge for more than a few minutes, but it should be enough to confirm the theory. Once confirmed, look around for a new battery.

If you do not have a universal external charger but you have a digital camera or another gadget with a Lithium battery and a charger, you can fashion a makeshift charger using that and a couple of wires. I have even used some rolled up aluminium foil from a chocolate wrapping for that purpose in the past. But be careful, you may cause serious harm if you do not know what you are doing.