I have a laptop and I want to start PC without typing password on startup.
To reiterate, you MUST authenticate by clicking on the closed lock in the bottom left corner of the Preferences dialogue and entering your administrator's password. If you don't do this, it won't work.
This isn't working for me. I have OS X Lion
I assume you are looking for automatic login:
1. open up System Preferences (top-left Apple icon)
2. go to Users & Groups
3. click on Login Options
4. select your username at "Automatic login"
By default these settings should be locked so you will have to click on the lock symbol in the lower left and enter the admins name and password. When selecting the account for automatic logon you will also be prompted for this users password.