hm...if you're the only user, you could try putting BIOS password protection on, if your BIOS supports the password to be asked when booting...but there are some problems with this, so I don't think this is the solution:
1) if the battery is removed for some time, protection won't work
2) you need to give this every time you boot - if the electricity gets cut off or your machine reboots for some reason, it won't get up without you
3) it's a harm for you
I'd say you get fed up with it quite quickly..