i have a dsl connection and i would like to make my internet inaccessible without a password how do i do that

Answer 1

unplug the modem when you are not around if you don't want anyone else on the internet when you are not there.
simple...
Another solution would be to put your computer in a room and buy a lock for the door when you are not there to supervise people screwing around with your computer.

Answer 2

When not using the computer, or DSL connection, turn off (or unplug) the modem.