In order for Kaleidoscope to display an audio file as a spectrogram, Kaleidoscope needs to perform a long series of calculations on the audio data and store the results in your computer's RAM. By default, Kaleidoscope limits the amount of RAM it uses at one time to prevent the program from hogging all of your computer's resources when it is displaying a file. This means that if you are viewing a relatively long file (depending on your sample rate), Kaleidoscope will only display a portion of it at a time.
If Kaleidoscope is only displaying a section of your file, the Viewer's menu bar will show you which segment you are viewing in parentheses, e.g. (1/8). You can use the "<T" and "T>" buttons to move between segments. You can also increase the size of the spectrogram Kaleidoscope can display by going to "File > FFT Settings" and increasing the Max Cache Size. Note that increasing the Max Cache Size will allow Kaleidoscope to use more of your computer's resources, potentially affecting the performance of other programs you may be using.