All the files on my Mac have vanished?

That's an extraordinary sequence of events, I must say. Do this:

Launch the Terminal application

(Applications -> Utilities -> Terminal)

then type in exactly the following:

  sudo periodic weekly

The system will ask you for your administrative password. Enter it. Then the script will take at least 5-10 minutes before it finishes, at which time you'll just be presented with another command line prompt.

Now you'll have rebuilt the "locate" database and I suggest you type in the name of a file or two that you used to have on your desktop but have lost, like this:

  locate "BIZ MEMO.pdf"

(that's a file currently on my desktop I'm using as an example, btw)

If you don't get any results then your files are truly gone, most bizarre, but I suspect you'll have them show up in a location other than where you actually are when you run the command, in which case you should be able to figure out if it's a different account or what else has happened to your system.

When you're done with the Terminal, type "exit" then Quit the application.

In any case, good luck. A very, very strange sequence of events!