wait!
it may not be the battery!
if you can restart withe the button, then it has nothing to do with the power supply (which is great!)
first I recommend checking if the prefs are the same.
you could even de-activate it, and then back to activate it just to make sure.
If that doesn't work, try zapping the P-RAM.
If that doesn't fix it, you could remove the int. battery and press the battery button, place the battery, and give it another try.
Even so, it may not be related to the battery...