nokia N91?

I think they do mention to make sure that the phone has enough power otherwise it will fail.
I know this will not help you now, that this happen.
The only thing I can suggest, to take it into repair shop - like Carphonewarehouse. If its in guarantee period - they will do it for free, if guarantee period is up - it maybe costly and they not always tell you how much it will cost before they take it in.
I was lucky with mine - it was still under guarantee by 1 month when this happen to me.

Sorry this may not be the best answer.

anna
November 2008