Hi Adriaan,

Do you see the area the waterfall should be - just below the spectrum display?  If the top edge of the waterfall has been pulled all the way down so all you see is spectrum a thick white line is displayed and you can move you mouse over it to enable the up/down arrows to drag it up to where you want.

Also, next to the spectrum display, upper right you should see the "Auto" button.  Click on it to reset the color or the waterfall.  The vertical slider may have been positioned to the top making the waterfall totally black.  Hit Auto, then adjust the slider to where the appearance is best for you.

73, Dale WB8CJW