uses
  ComObj;

function OpenConnection(ConnectionString: AnsiString): Integer;
var
  ADODBConnection: OleVariant;
begin
  ADODBConnection := CreateOleObject('ADODB.Connection');
  ADODBConnection.CursorLocation := 3; // User client
  ADODBConnection.ConnectionString := ConnectionString;
  Result := 0;
  try
  ADODBConnection.Open;
  except
  Result := -1;
  end;
end;

function DataBaseConnection_Test(bMessage: Boolean): AnsiString;
var
  asTimeout, asUserName, asPassword, asDataSource, ConnectionString: AnsiString;
  iReturn: Integer;
  OldCursor: TCursor;
begin
  OldCursor := Screen.Cursor;
  Screen.Cursor := crHourGlass;
  asTimeout := '150';
  asUserName := 'NT_Server';
  asPassword := 'SA';
  asDataSource := 'SQL Server - My DataBase';

  ConnectionString := 'Data Source = ' + asDataSource +
  'User ID = ' + asUserName +
  'Password = ' + asPassword +
  'Mode = Read|Write;Connect Timeout = ' + asTimeout;
  try
  iReturn := OpenConnection(ConnectionString);

  if (bMessage) then
  begin
  if (iReturn = 0) then
  Application.MessageBox('Connection OK!', 'Information', MB_OK)
  else if (iReturn = -1) then
  Application.MessageBox('Connection Error!', 'Error', MB_ICONERROR +
  MB_OK);
  end;

  if (iReturn = 0) then
  Result := ConnectionString
  else if (iReturn = -1) then
  Result := '';
  finally
  Screen.Cursor := OldCursor;
  end;
end;

procedure TForm1.Button1Click(Sender: TObject);
begin
  DataBaseConnection_Test(True);
end;