My son had Nokia N90 purchased on 25 Aug.05. On 28 June 2007 while travelling on a train he found network fluctuation and switched off the phone. After around 10 minutes when he tried to switch it on, it would not. There was a sputtering sound and the phone went dead. It could no longer be switched on. The phone was taken to authorised Nokia Care Centre who proclaimed it as "not reparable". Why such things happen? What went wrong: Could anybody enlighten me on this? In future what precaution should we adopt to avoid recurrence of such problem/misfortune?