Can't draw text to window

[MoosTone]

I'm just trying to output the value of a variable to a window.

Here is the function I run after a WM_PAINT message:

void OnPaint(HWND hWnd,MACHINE *machine)
{
    RECT  rect;
    PAINTSTRUCT ps;
    HDC hdc = BeginPaint(hWnd, &ps);

    GetClientRect(hWnd, &rect);
    SetTextColor(hdc, RGB(0xFF, 0x00, 0x00));
    SetBkMode(hdc, TRANSPARENT);
    rect.left = 10;
    rect.top = 40;
    char reg[10] = { 0 };
    DrawText(hdc,( LPTSTR )(_itoa_s(machine->cpu.AddressBus, reg, 16)), -1, &rect, DT_SINGLELINE | DT_NOCLIP);
    // SelectObject(hdc, oldPen);&reg
     //DeleteObject(hPen);
    EndPaint(hWnd, &ps);

I also do UpdateWindow(GetDesktopWindow)); in my main loop. Debug confirms the my paint routine is being run as it should.

Blank window is all I get

EDIT: Just realized UpdateWindow is being called, but after the initial window draw, WM_PAINT doesn't seem to be being sent. How do I force a redraw of the client area?