On login, I am only given the Guest user option. How do I log into my account? I tried to add a guest account to my laptop and when I restarted the computer, the only login option I have is the Guest Account.  Choosing this account restarts the computer into the Safari-only configuration.  There is no Systems Preferences available in this mode.

I did not unchoose my administrator account.  How did this happen?  And how do I get it back?
I think safe mode would work better. Here are the instructions, from the Apple Support website 


  To start up into Safe Mode (to Safe Boot), do this:
  
  
  Be sure your Mac is shut down.
  Press the power button.
  Immediately after you hear the startup tone, hold the Shift key. The Shift key should be held as soon as possible after the startup
  tone, but not before the tone.
  Release the Shift key when you see the gray Apple icon and the
  progress indicator (looks like a spinning gear).
  


Once your in, go to System Preferences and disable Find My Mac (iCloud settings) and Guest User (Users and Groups). Reboot. You should be able to login normally. If you would still like a guest user, just go back and enable Find My Mac.