Motorola i880 Sent Messages Problem - Help Please! 10 points for Best Answer?

[Jaclyn]

I have a Motorola i880 phone. For the past week for no apparent reason, every time I go down to 'Sent Items' and try to delete a sent message to make room, my phone's screen turns white and the phone shuts off. Why is it doing this? Is there any way I can fix this? Thanks in advance!