The default icon for Sequetron is black, so won't be visible
if your Windows desktop is also black.

To change Sequetron's icon to a white one:-
  Download the SequetronWhite.ico file to a location of your choice
  Right-click Sequetron's shortcut on the desktop
  Click Properties
  Click Change Icon...
  Click Browse... and select the downloaded icon file
  Click Ok

(actual steps may differ slightly depending on your version of Windows)

To revert to the original icon, repeat the above with the SequetronBlack.ico file.
(thanks to Richard Bowhall for this tip)