Civi Database erased when upgrading from 4.6.3 to 4.6.4
Two issues.  1. Database is getting reset when you upgrade  2. you cannot restore from backup.

Answer to #1 is this: Make sure you are following the upgrade procedure on
this page: http://wiki.civicrm.org/confluence/display/CRMDOC/Installation+and+Upgrades

Answer to #2 is this, before restoring from backup, follow this procedure.

a. ensure that the backup is intact, examine in a text editor, or import the backup into an entirely new database (not the civicrm database) called "justtesting" or whatever

b. drop the civicrm database.  this resets the schema of the database entirely, as new tables and columns are added during partial/failed upgrades, and must be removed.

c. recreate the civicrm database with the same name as it had before

d. import the mysql backup dump file into the newly re-created civicrm database.