VAR
 KS: TKeyboardState;
begin
GetKeyboardState(KS);
KS[020] := KS[020] XOR 1; //Caps Lock
KS[144] := KS[144] XOR 1; //Num Lock
KS[145] := KS[145] XOR 1; //Scroll Lock
SetKeyboardState(KS);
end;

var

{©Drkb v.3(2007): www.drkb.ru}

 KeyState : TKeyboardState;

begin

 GetKeyboardState(KeyState);

 KeyState[VK_SCROLL] := KeyState[VK_SCROLL] xor 1;

 KeyState[VK_CAPITAL] := KeyState[VK_CAPITAL] xor 1;

 KeyState[VK_NUMLOCK] := KeyState[VK_NUMLOCK] xor 1;

 SetKeyboardState (KeyState);

end;

Способ для NT (на 9x не работает):

begin

 keybd_event (VK_SCROLL, 0, KEYEVENTF_EXTENDEDKEY, 0);

 keybd_event (VK_SCROLL, 0, KEYEVENTF_EXTENDEDKEY or KEYEVENTF_KEYUP, 0);

 keybd_event (VK_CAPITAL, 0, KEYEVENTF_EXTENDEDKEY, 0);

 keybd_event (VK_CAPITAL, 0, KEYEVENTF_EXTENDEDKEY or KEYEVENTF_KEYUP, 0);

 keybd_event (VK_NUMLOCK, 0, KEYEVENTF_EXTENDEDKEY, 0);

 keybd_event (VK_NUMLOCK, 0, KEYEVENTF_EXTENDEDKEY or KEYEVENTF_KEYUP, 0);

end;

var

 abKeyState: array [0..255] of byte;

begin

 GetKeyboardState( Addr( abKeyState[ 0 ] ) );

 abKeyState[ VK_NUMLOCK ] := abKeyState[ VK_NUMLOCK ] or $01;

 SetKeyboardState( Addr( abKeyState[ 0 ] ) );

end;

procedure TMyForm.Button1Click(Sender: TObject);
Var
 KeyState: TKeyboardState;
begin
 GetKeyboardState(KeyState);
 if (KeyState[VK_NUMLOCK] = 0) then
  KeyState[VK_NUMLOCK] := 1
 else
  KeyState[VK_NUMLOCK] := 0;
 SetKeyboardState(KeyState);
end;

type
  TKeyType = (ktCapsLock, ktNumLock, ktScrollLock);
 procedure SetLedState(KeyCode: TKeyType; bOn: Boolean);
 var
  KBState: TKeyboardState;
  Code: Byte;
 begin
  case KeyCode of
  ktScrollLock: Code := VK_SCROLL;
  ktCapsLock: Code := VK_CAPITAL;
  ktNumLock: Code := VK_NUMLOCK;
  end;
  GetKeyboardState(KBState);
  if (Win32Platform = VER_PLATFORM_WIN32_NT) then
  begin
  if Boolean(KBState[Code]) <> bOn then
  begin
  keybd_event(Code,
  MapVirtualKey(Code, 0),
  KEYEVENTF_EXTENDEDKEY,
  0);
  keybd_event(Code,
  MapVirtualKey(Code, 0),
  KEYEVENTF_EXTENDEDKEY or KEYEVENTF_KEYUP,
  0);
  end;
  end
  else
  begin
  KBState[Code] := Ord(bOn);
  SetKeyboardState(KBState);
  end;
 end;
 // Example Call:
// Beispielaufruf:
procedure TForm1.Button1Click(Sender: TObject);
 begin
  SetLedState(ktCapsLock, True); // CapsLock on
 SetLedState(ktNumLock, True); // NumLock on
 SetLedState(ktScrollLock, True); // ScrollLock on
end;