hello everyone...

i have a SE k850i, its been a year now i have been using this phone and all of a sudden it has started giving a strange problem ... its like this .. when i touch the keypad the screen goes blank and after a while it comes back by itself without restarting .. and when i try to unlock and view anything it again gets blank ... i really dont understand why this is happening ..but would certainly wold want to know why .. and try rectifying it.....someone please help me out.....