You can’t access a SQL Server without a password.
You can change the password of a SQL account using sp_password. Windows logins passwords would be changed at the Windows Domain level by the user.
The SA account is a default account which is created when the SQL Server is installed. This account has full access to the system and should only be used for a backup in case all other accounts which
have sysadmin rights to the instance are locked out.
You Can access SQL server without a separate SQL Server password if:
– You are loged on to the server SQL Server is running on with local administrator rights (localy or through RDP) and connect to SQL Server using Windows Integrated authentication
OR (if remote connections are enabled in SQL server)
– You connect to the SQL server from a other Windows server or client using Windows integrated Authentication with an account that is member of the local admin group of the Server SQL Server is running on (for example if the Domain admins group is a member of the (windows) local administrators group of the server SQL Server is running on, this would be any account that is a member of the domain admins group. This is a common configuration for domain member servers)
By default the windows local admin group of the Server SQL Server is running on is a member of the Sysadmin role in SQL Server. (Pre SQL 2008)
ofcause if everything on the Windows side is correctly configured you still need a password to login to Windows itself as a Domain Admin or local Admin