Add properties in Objects Tools has disappeared

Hello, this is my first post, i’m sorry if my question is low level.
I am working in Blender and since yesterday, in version 2.56, adding a new mesh, such as a triangle, it doesn’t give me options to modify the original mesh, i can’t see the add properties in the tab Tool Shelf (T - Key).
So, i can’t choose the numbers of sides or vertex or the scale of the mesh.
I supose it will be a big mistake or a great nonsense, but I’m going crazy.
Please, help ??

You can press F6 instead. You may see a small ‘+’ in the bottom right corner of the 3d view. Press this to show the operator settings at the bottom of the toolshelf.

THANKS Richard
You have a new friend now…