[RESOLVED] One thread stop all system!! How avoid it? :(

[AKE]

Windows 7. Only mouse work and the thread.
What incorectly??

 WriterThread = (HANDLE) _beginthread(Writer, 0, NULL);

void Writer(void *args)
{
  Writing = TRUE;
  Stop    = FALSE;
  HANDLE hf;
  HWND hProgress = CreateWindowEx(0, PROGRESS_CLASS, NULL, 
		               WS_CHILD | WS_VISIBLE,
			      20, 20, 260, 17,
			      hwnd, NULL, hInst, NULL);
 
  if (InitPort())
  {
	MessageBox(hwnd,L"asdfasdf", L"asdf", 0);         
	Writing = FALSE;
    return;    
  }
  hf = CreateFile(FileName,          
                    GENERIC_READ,
                    0,
                    (LPSECURITY_ATTRIBUTES) NULL,
                    OPEN_EXISTING,
                    FILE_ATTRIBUTE_NORMAL,
                    (HANDLE) NULL);
  if (hf == INVALID_HANDLE_VALUE)
  {	     
	MessageBox(hwnd,L"asdf", L"asdf", 0);         
	Writing = FALSE;
    return;	 
  }
  DWORD sz     = GetFileSize(hf, NULL); // asdfasdf
  unsigned CycleCount = sz/(256*20);
  SendMessage(hProgress, PBM_SETRANGE, 0, MAKELPARAM(0, 20));
  DWORD tmpBytesRead;
  DWORD Written;
  int szName = strlen(TempName);
  if (!WriteFile(hComPort, TempName, szName, &Written, NULL))
      {	     
 	    MessageBox(hwnd,L"asdf", L"Ошибка", 0);         
 	    Writing = FALSE;
        return;	 
      }
  if (!WriteFile(hComPort, &STX, 1, &Written, NULL))
	  {
	    MessageBox(hwnd,L"asdf", L"asdf", 0);         
		WriteFile(hComPort, &Eof, 1, &Written, NULL);
	    Writing = FALSE;
        return;
	  }
  int ProgressPos = 0; 
  unsigned Index = 0;
  int CycleIndex = 0;
  char buff[256];
  int ReadSize = 256;
  while (Index < sz)    
  {
    SendMessage(hProgress, PBM_SETPOS, ProgressPos, 0);
	CycleIndex++;
	if (CycleIndex == CycleCount)
	{
	  CycleIndex = 0;
	  ProgressPos++;
	}
    if (Stop)
	{
	  WriteFile(hComPort, &Eof, 1, &Written, NULL);
	  Writing = FALSE;
	  CloseHandle(hf);
	  CloseHandle(hComPort);
	  return;	   
	}
    if ((sz-Index) < 256) ReadSize = sz-Index;
    if (!ReadFile(hf, buff, ReadSize, &tmpBytesRead, NULL))
	{
	  MessageBox(hwnd,L"asdf", L"asdf", 0);         
	  WriteFile(hComPort, &Eof, 1, &Written, NULL);
	  Writing = FALSE;
	  CloseHandle(hf);
	  CloseHandle(hComPort);
	  return;
	}
    if (Stop) // asdf
	{
	  WriteFile(hComPort, &Eof, 1, &Written, NULL);
	  Writing = FALSE;
	  CloseHandle(hf);
	  CloseHandle(hComPort);
	  return;	   
	}
    if (!WriteFile(hComPort, buff, ReadSize, &Written, NULL))
	{
	  MessageBox(hwnd,L"asdf", L"asdf", 0);         
	  WriteFile(hComPort, &Eof, 1, &Written, NULL);
	  Writing = FALSE;
	  CloseHandle(hf);
	  CloseHandle(hComPort);
	  return;
	}
	Index = Index + ReadSize;
  }
  WriteFile(hComPort, &Eof, 1, &Written, NULL);
  Writing = FALSE;
  CloseHandle(hf);
  CloseHandle(hComPort);
  MessageBox(hwnd,L"asdf", L"asdf", 0);
  return;
}