BLACKBERRY BOLD 9900 unlocked software fault !

bb bold 9900 unlocked to all networks. started playing up. loads up fully and when comes on to main screen it stays on for a few seconds and switches off. done an update on laptop and got it working but reset the phone and gone back to normal. 120 NO OFFERS NO SWAPS dont bother texting if ur not going to pay 120 as you will wasting both of our times. text pls as busy, will get back to u asap collection cannock or can deliver if not far