Depends on what browser you are using. The Function keys are generally what control the Top Navigation Bar, so pressing F11 or F12 often will bring back your top Navigation bar. I find this works for me when i'm using Internet Explorer 7
There are two ways that I know of. One way is to right click where your menu bar is and you should a list that shows you what you have in use and navigation bar is the second one. The other is you go to view then tollbars and it will show you there.