You need to right-click on the play button and select "play to end of file" instead of "play to end of screen" (the wording may vary, I'm not in front of the program right now).
Or, right above your wave files, there's a green bar, put your mouse to the right end of it and drag it until you see the entire wave file in your window...
i taught myself the program, only 4 months under my belt,
u might be pressing the wrong button.
the western play arrow, only plays the selction your viewing, the play buttun w/ the circle around it to the right is to play to the end of the tracks.
OR hit the button that has a right-pointing arrow in a circle (which will cause it to play to the end of the song, not just to the end of what's displayed on the screen
OR hit Alt/right arrow to squeeze the whole waveform onto the display and hit "play"