missing gui desktop ?

So, today, I reboot my computer and when it came back up, the desktop picture and most of the menus were missing. All I have is a funny looking clock, firefox, and the console. That is all I have. The thing I don't understand is that I didn't change ANYTHING before rebooting my computer. I tried rebooting it several times and each time the same screen shows up. I am currently running Fedora 7.
Does anyone know what happened? This is not the first time it happened. It's happened several times before and I had to re-install Linux from scratch before. It is really annoying me.
Thank you.