Buttons not working on W580I

For some reason a few of the buttons are not working correctly on my phone. When the phone is slid open and the screen is lit up the 4, 7, 9 * & # keys do not work, however if I leave the phone so the screen goes blank then I can press the button, it registers on the screen and the phone lights up again.
As this is the case I believe it may be a software issue rather than a wiring problem and thought that re-installing my firmware or even updating it may help.
However I am new to this and haven't a clue what to do. So any help would be well appreciated

Is ur set still under warranty cover?? If it is then u should hand it over to the service center. Otherwise its a wise idea to give firmware flashing a try.

unfortunately it is out of warranty. would like to flash the firmware but unsure how to!!!!