Help! Objects disappear from scene view

Yesterday I was taking a look at the "Edit-Preferences" and whenever I changed a setting, the background color of the scene viewer changed from black, to bright red, to dark red. And then all the objects disappeared! If I drag a new object I can see it on the scene viewer but not the old ones! If I run the game everything is ok, but I need to edit old objects and now I can't see them...

I also installed Adobe Flash CS3 yesterday, could it have anything to do with it?

Help is most welcome. Thanks