if(active_click = true) then
  begin
    Form8.Left := Mouse.CursorPos.X-Form8.Left;
    Form8.Top := Mouse.CursorPos.Y;
  end;

...
var
  md : Boolean;
  mp : TPoint;
...
procedure TMainForm.PanelHeaderBarMouseMove(Sender: TObject; Shift: TShiftState; X, Y: Integer);
var
  P : TPoint;
begin
  if not md then Exit;
  P := Point(PanelHeaderBar.Left+(X - mp.X),PanelHeaderBar.Top + (Y - mp.Y));
  P := ClientToScreen(P);
  P.Y := P.Y - (Height-(ClientRect.Bottom-ClientRect.Top))-PanelHeaderBar.Top;
  Left := P.X;
  Top := P.y;
end;
...
procedure TMainForm.PanelHeaderBarMouseDown(Sender: TObject; Button: TMouseButton; Shift: TShiftState; X, Y: Integer);
begin
  md := True;
  mp := Point(X,Y);
end;
...
procedure TMainForm.PanelHeaderBarMouseUp(Sender: TObject; Button: TMouseButton; Shift: TShiftState; X, Y: Integer);
begin
  md := False;
end;

{ = DragAndDrop = }

var
 xPos, yPos: integer;

procedure TForm1.FormMouseDown(Sender: TObject; Button: TMouseButton; Shift: TShiftState; X, Y: Integer);
begin
 xPos := x;
 yPos := y;
end;

procedure TForm1.FormMouseMove(Sender: TObject; Shift: TShiftState; X, Y: Integer);
begin
 if HiWord(GetAsyncKeyState(VK_LBUTTON)) > 0 then
 begin
  Form1.Left := Form1.Left + X - xPos;
  Form1.Top := Form1.Top + Y - yPos;
 end;
end;