Windows Vista. AE CS6. Just installed. I write text on a text layer--the text is invisible. I make a shape--the shape is invisible. In each instance I can see the bounding box.
Weird thing. When I hit the view rulers, the objects become visible for a short time, then disappear again. That only happens once.
When I purge memory, the damn object becomes visible again. Then it soon disappears again. I can repeat this.
Almost certainly Open GL problems. Try turning it off for preview. Try updating your drivers. You've got about a zillion different graphics cards available. It would help if we knew which one you were using.
And you may also try to set the comp quality to Final Rendering to revert to software mode....