procedure TForm1.Button1Click(Sender: TObject);
var 
  DC: THandle;      // display context
  Bits: integer;    // bits per pixel
  HRes: integer;    // horizontal resolution
  VRes: integer;    // vertical resolution
  DM: TDevMode;     // to Save EnumDisplaySettings
  ModeNum: longint; // video mode number
  Ok: Bool;
  fre: integer;     // refresh rate 
begin 
  DC   := GetDC(Handle); 
  Bits := GetDeviceCaps(DC, BITSPIXEL); 
  HRes := GetDeviceCaps(DC, HORZRES); 
  VRes := GetDeviceCaps(DC, VERTRES); 
  fre  := GetDeviceCaps(DC, VREFRESH); 
  // Show Current Resolution 
  Edit1.Text := Format('%d bit, %d x %d', [Bits, HRes, VRes]); 
  ReleaseDC(Handle, DC); // Show all modes available ModeNum := 0;  // The 1st one 
  EnumDisplaySettings(nil, ModeNum, DM); 
  ListBox1.Items.Add(Format('%d bit, %d x %d bei %d Hz', [DM.dmBitsPerPel, 
    DM.dmPelsWidth, DM.dmPelsHeight, Dm.dmDisplayFrequency])); 
  Ok := True; 
  while Ok do 
  begin 
    Inc(ModeNum); // Get next one 
    Ok := EnumDisplaySettings(nil, ModeNum, DM); 
    ListBox1.Items.Add(Format('%d bit, %d x %d bei %d Hz', [DM.dmBitsPerPel, 
      DM.dmPelsWidth, DM.dmPelsHeight, Dm.dmDisplayFrequency])); 
  end; 
end;