Check if the Alarm LED is on. If so, the Paper Cassette may be out of paper or not properly installed. If it is empty, load a new stack of paper into the Paper Cassette.
If there is paper in the Paper Cassette, make sure that it is straight. If the paper is curled, you should straighten it before printing. Sometimes it is helpful to remove the paper, turn the stack over, and then reload it in the paper tray.
Reduce the stack of paper in the Paper Cassette, and then try again.