This is going to be a little redundant, but do the following and let's see if your settings keep changing back.
-Click Start, and then click Run. In the Open box, type control userpasswords2, and then click OK. In the dialog box that appears, enable Users must enter a user name and password to use this computer check box, and then click OK.
-Click Start, Run and type rundll32 netplwiz.dll,ClearAutoLogon (you may not see anything happen, it's ok)
-Open Registry Editor (Regedit.exe) and navigate to: HKEY_LOCAL_MACHINE\Software\Microsoft\WindowsNT\CurrentVersion\Winlogon, Verify that the DefaultPassword entry is not there and that AutoAdminLogon is set to 0
-Reboot, you should have to enter your password (just as you did last time you changed the registry). Once you're logged in, reboot again and see if you still have to enter your password.
i follow your suggestion first i check "Users must enter a user name and password to use this computer"
i type "rundll32 netplwiz.dll,ClearAutoLogon" -i type it exactly in quote.it gives me error message
i set "AutoadminLogon to 0"
i reboot computer five or six times. to make sure that everythings is ok...
eventhough it gives me error message but it's seem everything is OK...... Now...
no more lonon box message annoying me anymore just boot straight to welcome screen ^.^
Thankyou for your kindly help.