Well...
After recovering from a panic attack after thinking I'd bricked mine... (about 20 mins ago) after trying to change the handshake animation and sound to non standard after hacking the phone... (see symbian-freak) ...
I couldn't get mine past the Nokia word on white back drop on startup. I'd changed the save location of the startup.mbm and the phone couldn't find it... wouldn't start up...
Anyway to cut a long story short, I only got it back on by...
With the phone off, press and hold the green button, 3 and # all simulataneously, while doing so press the power button and release while still holding the other three. Do this until the phone comes on.
See if that helps.