Almost all elements have suddenly disappeared in the model. Just some elements are visible in the view.
A displayset was created by accident and just this displayset is displayed in the view. When setting off this displayset all elements will be visible again
Option 1:
View Attributes > Displayset to be turnt off
Option 2:
Keyin: SET DISPLAYSET OFF
http://communities.bentley.com/communities/other_communities/askinga/w/askinga/named-groups-displaysets-and-quick-sets