In reply to tlm:
You left yourself logged in.
As for the backup, unless you're storing insane amounts of movies or something, store your stuff on a flash drive instead of a regular external hdd. I've got documents stored on a 128mb stick that I had like 10 years ago and it's still fine, presumably because it's only ever running for a few mins at a time.
On the other side of thing I've got 3x 1tb drives that I've had for over 5 years that are still running just fine, though they are USB, don't know anyone that uses firewire for anything.