[dINGO]

This is probably something I misconfigured, but I cannot seem to fix it (I am a only a 7 mo convert to macs).

I do a full backup to a usb hd (seagate freeagent)

If I have the usb hd attached on starting the mac, the mac boots from the usb hd automatically. (Now, I used to have SD set to make the backup a start up disk, but I changed that to just shut down computer, but the problem continues).

The problem is if I don't realize this is happening and work on the mac, things are just getting saved on the usb hd which will be wiped on the next backup. This is very bad.

Any ideas why the usb hd is the default startup volume / disk, and how to change this.

TIA