Why have the buttons stopped working?

Hi, I have got a Sony Ericcson W880i and the green button, 7, 8 and 9 buttons have just suddenly stopped working, so this means I am unable to dial numbers that contain them numbers and can not text either...I only brought the phone about 3 months ago and didnt think anything of it and threw the reciept away, anyone else had this poblem with their buttons??? I dont really want to have to send it away to get fixed as I know it will cost a bomb.

I have tried downloading and updated software using a usb lead but still no joy, I have tried turning it off and on, the only thing I havent done is thrown it against a wall (yet)

Thanks for any help I may get