Unfortunately, these things do happen. Best thing to do is call AP customer support on Monday and ask them for suggestions to make sure you've tried everything, but the suggestions I remember hearing are:
- Make sure you're using a stylus, not the pad of your finger. The pointy end of a cheap Bic pen cap, or the clicker button on a retractable ball point pen, or something similar, should work well enough.
- Using a fine-pointed or flat object like a toothpick or a shirt collar stay or something like that, carefully go around the edge of the screen, just under the bezel, and make sure there is no debris / crud built up that could be confusing the screen digitizer
- Power the unit via the plug-in adapter and make sure it's up to room temperature (not too hot or too cold)
- The upside-down trick you've already tried
I'm sure the AP tech guys have another trick or two up their sleeve. Good luck!