I can see my Wall but my friends cannot see it. My friends say that my Wall is gone or that I have no Wall.

There's a setting to control who sees your Wall on the "Sharing on Facebook" section of the Privacy Settings page. To check your settings for this feature, follow the "Customize settings" link at the bottom of this section. Right now, you probably have the box next to "Allow friends to post on my Wall" unchecked or have the "Wall posts by friends" section set to "Only Me." In order to show your friends your Wall, make sure the "Allow friends to post on my Wall" is checked and adjust the privacy of your "Wall posts by friends" feature to a less restrictive setting.