My Book Essential 2.0 / Microsoft Backup Wizard won't display

 I have backed up my computer to my external hard drive several times before by going to control panel, performance & maintenence, backup data - at which point the Wizard pops up.
Today when I click 'backup data" I get the little hour glass for a few seconds but the Wizard screen never comes up.  I have tried going through Start - accesories- system tools - backup - but still nothing.  If the Wizard was somehow disabled, how can I reenable it.  My system is Windows xp media center version 2005.   What could have happened to the backup wizard?  I can’t find it under add and remove programs.  Should I try restoring to the end of Dec. (that is the farthest back date option I seem to have)? I last did a back up to the external hard drive 11-21-09.   Last week an auto update restarted my computer - would that have removed this wizard?
Please help.  Thank you