Could be lots of things, Geoff, including a problem with your graphics or
sound cards, other programs you happen to be running at the time or even
snow within the game play.
You may want to go into Control Panel/Administrative Tools/Event Viewer and
click on the Application list in the left panel. Then look in the right
panel for any yellow triangles with exclamation points or red circles with
white x's in them. You can right-click those and see a portion of the error
message, which might give you a clue to the problem.
