procedure TForm1.Button1Click(Sender: TObject);
var
  w: dword;
  Root: string;
  i: integer;
begin
  w := GetLogicalDrives;
  Root := '#:\';
  for i := 0 to 25 do
  begin
    Root[1] := Char(Ord('A') + i);
    if (W and (1 shl i)) > 0 then
      if GetDriveType(Pchar(Root)) = DRIVE_CDROM then
        Form1.Label1.Caption := Root;
  end;
end;