I have tried leaving it to charge for over an hour with no luck (wont get past the NOKIA logo)
I have not installed any 3rd party operating systems on the phone at all.
I can get the flasher to see it and if I do flasher -R to reboot it, it displays the NOKIA logo with a USB logo then it disappears back to a dark screen and the charging LED. If I run lsusb, it just says "N900 (Storage Mode)"

Is there some way I can tell whether my battery is flat (and just needs to be left overnight to charge or something), whether my battery is dead (and isn't properly charging) or whether my phone needs re-flashing somehow?