thanks for the responses so far.
Yes, different cables, different ports, different computers, all with the same results unfortunately.
File was named properly and, to make sure i covered all the bases, completely formatted the card, fat32.
phone sees the file, says 'loading' then just reverts back to bootloader screen.
As far as I know its completely charged. I've had it connected to the comp, and just to be sure, a wall outlet with a 'charge only' cable.
I've run out of ideas.