I experienced the same problem with the Start Menu not appearing when I pressed the Windows key. My issue was keyboard-related. I have a gaming keyboard with different gaming modes. One of those modes apparently disabled the Windows key! Switching modes solved my problem.
For reference, my gaming keyboard is a Mad Catz v7. To switch modes, I pressed the red button that looks like 4 tiger stripes. Hope this helps. Start10 is a fantastic app.