Proplem with keyStroke (ALT-x)

I try to use this code:

Code:

AnsiString strWindowName = "Element Client";
HWND windowHandle = FindWindow(0, strWindowName.c_str());
	if (windowHandle)
	{
	SendMessage(windowHandle, WM_SYSKEYDOWN,0x12,0x20380001);
	SendMessage(windowHandle, WM_SYSKEYDOWN,0x33,0x20040001);
	SendMessage(windowHandle, WM_SYSCHAR,0x33,0x20040001);
	SendMessage(windowHandle, WM_KEYUP,0x12,0xc0380001);
	SendMessage(windowHandle, WM_KEYUP,0x33,0xc0040001);
	}

to send ALT-3 to application, but nothing happen. but if i hold ALT button until that code ran , it'll effect. Can someone tell me why is that?

Or show me how to send KeyStrokey by use Send/PostMessage Function.

Thank You