1.) Press the "INFO" button on the back of the camera. Press it repeatedly and it should cycle through the different modes. One of the modes is actually "LCD OFF", so that could be the culprit.
2.) Also make sure that the rubber "eyecup" padding has not slid up 1/4 inch and covered the "display off sensor" that turns the display off when you put your face up to the camera. If that rubber eye pad (or dirt or makeup or your thumb or anything else) is covering the sensor, then the display would turn off thinking you have the camera up to your face.