I have a Motorola Triumph. I'm new to android phones and was learning to use it, but now after I dial, the screen goes black and I can't hang up. Can't get voice messages because I can't enter my password on a blank screen. If I make a mistake in trying to remove a call from the call log and the phone dials instead of letting me delete the call from the log, the screen goes black and I can't hang up except by remove the battery. The phone is not particularly useful this way. Help appreciated.