Hi edagro,
This is the BIOS setting that tells the system what to do if the power goes out and comes back on. "Off" means it stays off, and "on" means when the power is restored, the computer turns on. "Last" means it remembers the previous state and resume that when power is restored.
For most home users, the setting should be set to off to prevent the system from trying to boot during periods of power surges.
