Plot Display

Hi, I have installed Mathcad 14 and it is working, but standard 2D plots (so far, haven't tried 3D yet) do not display correctly (the blue 'hatch' pattern is displayed where the plot should be). The 1st plot displays fine, but subsequent plots do not - is this a Windows 7 problem? I am running it on a HP d7t-3085 i7 core with an Nvidia 230M GT video card. Thanks, Michael