Nokia mobile1200
Message inbox not open.when i try that to open it then mobile restart automatically

I have nokia 1200.when i open inbox massage folder then my mobile automatically restart.what is that problum and how to solve it.i have so many masseges pending for delete.after this problum i do that option all read messages delete.but there is no responce.please tell me how can i solve that problum.this problum occured only on inbox and further folder open on one click.