The following checks that you have values for each of the four variables:

if(($Instance) -and ($uname) -and ($pwd) -and ($newpwd))

{

$srv = new-object ('Microsoft.SqlServer.Management.Smo.Server') $Instance

#This sets the sql authentication

$srv.ConnectionContext.LoginSecure=$false;

#This sets the login name

$srv.ConnectionContext.set_Login($uname);

#This sets the password

$srv.ConnectionContext.set_Password($pwd)

}

else

{

# Handle missing value(s) condition.

}