My PC has just one admin account but when I entered in Safe Mode using "msconfig" command there was another administrator account without password and profile full name.The name of 2nd account is "Administrator".
I bought old computer.Did old user create this account?Or is it default hidden account of XP?
I'm going to disable 2nd admin account by ComputerManagement/LocalUsersandGroups/Users command.

The account named Administrator is most likely the default full admin account.
Sounds like the previous owner created another account with admin abilities.