The first thing you need to tell us is what Mac OS are you using? Snow Leopard, Lion, Mountain Lion, and Mavericks are the most recent ones.
Secondly, if you do not have any installer DVDs, the Command+S "method" only works with Leopard or earlier. However, this method does not let you reset the password. It lets you create a new user account I(like you did when you first got your machine), and then you create a password (write it down somewhere safe, just in case you need it again!).
If you happen to know the short name of the user name, then you could do it via Terminal. Since your machine is still on, here is the way to do that:
"
Reset Admin Password Using The Terminal
You can reset the password by printing out (or writing down) and carefully following these steps.
First, find the short name of the admin user on the machine. The easiest way of doing this is by looking at what the directory is called in the Users folder.
Now, start in
Single-user Mode. It should boot into a command line.
Enter these
exact lines. Press RETURN after each.
mount -uw /
ifconfig lo0 up
cd /var/db/netinfo
netinfod -s local
Now you'll need that short name. Enter "passwd", a space, and the short name of the admin. For example, if the admin was rather prosaically called "
imadmin", you would enter "passwd
imadmin".
The computer will now prompt you to change the password for "
lmadmin" (or whatever the short name was). Go ahead and enter a new password.
Now, enter:
sync
reboot
and the machine will reboot. The admin password should now be changed."
Note that it says CAREFULLY, and that you must enter those terminal commands EXACTLY like it says, and to press RETURN after EACH such command.
