HTC EVO 4G gets an OTA upgrade to repair camera bug
While the carrier has not provded any change log, it is expected that the new firmware will fix the bug that turns the phone off and back on when the user accesses Qix or Tango. The repeating power cycling could have required a hard reset to correct which would have resulted in the loss of all of your stored memory. Hopefully the new OTA upgrade will do the trick instead.
source: Sprint via AndroidCentral