Still trying

It looks liek I am almost there.

The program builds with no errors.
When I execute it the following happens:
Before doing anything I opened the Task Manager and I see Martin1.exe CPU=0
When I send a char into the serial port the CPU=50 and nothing happens.
Any char, even the 0x31 causes cpu=50 and nothing happens on the dialog.
The MessageBox doesnt appear (for testing purposes ONLY).
I can still click buttons on the dialog that do work so it's not hung.
I know for sure I am doing something wrong.
Thanks for the help so far.

Below I think are the pertinent parts of my app.
==============================================================

In Martin1Dlg.h I added near the top:

#define MY_WM_MESSAGE1 (WM_APP + 1)

In "class CMartin1Dlg : public CDialog" I added just above protected:

  afx_msg LRESULT OnMyMessage1(UINT wParam, LONG lParam);

==============================================================

Near the top of Martin1Dlg.cpp I have:

UINT WorkerThreadProc( LPVOID Param );

==============================================================

In the message map I added the line before "END_MESSAGE_MAP()"

BEGIN_MESSAGE_MAP(CMartin1Dlg, CDialog)
  //{{AFX_MSG_MAP(CMartin1Dlg)
  ON_WM_QUERYDRAGICON()
  ON_BN_CLICKED(IDC_BUTTON1, OnButton1)
  //}}AFX_MSG_MAP
  ON_MESSAGE(MY_WM_MESSAGE1, OnMyMessage1)
END_MESSAGE_MAP()

==============================================================

In OnInitDialog() before the "return TRUE" I added:

  AfxBeginThread(WorkerThreadProc,NULL,THREAD_PRIORITY_NORMAL,0,0,NULL);

==============================================================

Routine to handle the message:

LRESULT CMartin1Dlg::OnMyMessage1(UINT wParam, LONG lParam)
{
  AfxMessageBox("Got here");
  return 0;
}

==============================================================

The worker thread:

UINT WorkerThreadProc( LPVOID Param ) //Sample function for using in
AfxBeginThread
{
  int DataByte=0x00;
  int Count=0;

loop:
  while(Count == 0){
    Count = Port.BytesInReceiveBuffer();
    Sleep(100);
  }
  DataByte=Port.GetByte(18);
  if (DataByte == 0x31){
    ::PostMessage(HWND_BROADCAST, MY_WM_MESSAGE1, (WPARAM)0, (LPARAM)0);
  }

  goto loop;

  return TRUE;
}