Edit Mode Disappears

I am new to Blender so please forgive me if this question seems ridiculous. But, I am attempting to create a polygon model in 2.5. I have inserted my background image successfully. When I do, the only mode that is available is Object Mode. I do not know how to get the edit mode back. I have “tabbed” and it still does not allow me to go into edit mode. As a matter of fact, they all disappear except the object mode. Can someone please help me with this?

make sure you have selected an editable object and not the camera or a lamp

Thank you so much! I told you I was new. Please forgive my inexperience. I will get there.