pbm in sony k790i new.. plz help me frnds

i find that my new k790 i purchased on 26 december 2008 hangs by returning a blank screen after long duration calls exceeding more thn 30 mins. my standby screen becomes blank and i m unable to navigate into the menu screen and also i m unable to switch off the mobile. my memory stick is a 2gb card whis is at present 1524mb free. it is a brand new phone and i m finding it odd.. please help me and suggest me the ways to solve this problem.. let me know why this happens and also the way out.

try to reflash it buddie se if that solves the problem there are tuts on here showing u how to do it

dude thanks but i tried to update my mobile using somy update solution as found in 1 of the threads.. it replied tht my sw is an updated 1. i gave it a reinstallation.. till the problem is there.. plz tell me wht to do.. looking forwar for ur help pal