When I turn on my N800 it shows the white screen with the Nokia logo, and just stays like that for around 30 seconds before turning off. No progress bar.

Have attempted to flash, enable R&D mode, etc using flasher-3.5 but in all cases the flasher won't recognise the device ("Suitable USB device not found, waiting.").

It's not a PC/software/cable issue as I can successfully run the flasher with -i on another N800 and that works fine (pressing home while turning on, after starting the flasher and then plugging in USB).

I never get the USB logo when I turn on while pressing the home key.

Have tried removing the battery and leaving it for a while before trying again.

The battery is fully-charged - charged on a known working N800 first. I have also tried with the battery of a known working N800.

Memory cards all removed.

Any suggestions on what to do next? Or is it dead?