The main window is not being drawn therefore you are seeing what is originally under it, inside your window. You need to go back to VMK 3 and fix the source code before continuing.
Setup a breakpoint in your code where you create your window and step through line by line using the debugger: http://www.marek-knows.com/downloads.php?vmk=cpp13
Look for any logic errors or variables that have invalid values. Also, make sure you check the return value for each function to be certain that the function did not fail on you.
If you suspect m_hDC is invalid, have a look at it's value in the debugger. Before you use it, it should have been already set. Double check the VMK to make sure you didn't miss any lines of code.