i have a problem....

... just installed grasshopper. When i want to "set one point" the point itself is not displayed in the rhino-window (if i attach a note-sheet i can see the coordinates). But i can't see the green or red crosses i used to see.

I must admit i'm just getting started with grasshopper - this is probably a very obvious mistake.
Do i have to install again (or just change some settings)?
Does anyone know?
Thanks,
Christopher