OK, it appears that removing the nokia SD card, plugging into charger, then doing a few reboots has solved the problem. I didn't have the little metal "holder" on the SD card so perhaps it was moving around and shorting out.

My N800 won't start by just pressing the power button, though. Like some other user mentioned I have to double-tap the home key to get the blue light to come on.. then it will power up using the power button.