Screen Flickering after a restart

Hi,

Yesterday while video chatting the phone just hung on me and started to vibrate with a white screen. After a minute the white screen was replaced by mutiple couloured lines and the borders turned black and the phone kept vibrating.After a half an hour there was a oval shaped ring in the middle part of the screen and was flickering. After the battery died down and the vibration stopped. After a brief amount of charge the phone started working normally but the oval ring stayed and the screen flickers a lot. i had done a factory restore which upgraded it to IOS6 but no luck. I turned off the phone for the entire night and the oval band almost disappeared but the screen flickers a small amount in the upper half. Any idea if its hardware or a software issue.