Q: What did you do?
A: You've selected the tree and zoom it out so much that is to small to be shown on the screen.
Solution: Pres F3 and scroll down or up your mouse wheel until a slide bar appear on the left side of the screen. If this doesn't happen you must press once again F3 and redo the...
Starting with R19 it is possible to create a dynamic sectioning in a CATPart. It's a simple way for sectioning a part, without copy it into an assembly.
So, you have to Right Click somewhere on the toolbars and choose Customize. Now go on the Commands tab and click on All Commands from the...