Recently, i was configuring one of my Moodle sites.  I was trying to hide the admin menu from students.  Well some how I ended up hiding the “administration” block from everyone including me… the admin! The only way I could undo it was to go into the SQL table and change the “mdl_block_instances” table, find the record with the with the “blockname” – “settings”, and change the value in the “pagetypepattern” field to “*”.  I had some pages listed there.  Once I did that it reappeared!