i have the same problem. Reboot even on regular charger.
i tryed to reflash, but i press "u" and when nothing happens, one time the computer found the Nokia USB ROM and get a error on Driver. Flasher still in "Suitable USB device not found. waiting."

I tryed Windows 7 x64, Windows 7 x86 and Ubuntu 9.10 x86. All the same problem. unless in Ubuntu, when i never get error with driver. but, doesn't works too.

HELP!