P3D v3 started crashing for me today when I try to load an A2A C172 with Mindstar GNS430. It has been running fine for a couple of years until today. The C172 without Mindstar loads fine. I'm running Windows 10.

Any idea how to fix this?

Things don't just quit working cuz... so, the question is... what have you changed on your system?  First, I hope you are loading Prepar3D with the default flight (F22) active... not saying you have to load into the flight, just that it's what shows up as the default when you go to the setup screen to make/choose a flight.

Second, did you add any additional software, update any modules (FSUIPC as example), modify scenery?

I had made no changes at all on the computer between the last time it worked (the day before) and when it started crashing. No, I had my default start up my A2A C172, not the F22. It had been working for at least a couple of years (since I first purchased the Mindstar GPS). But even when I start P3D with the default F22, it makes no difference. As soon as I try to load the C172 with Mindstar, P3D crashes. If I load the C172 without Mindstar enabled, it doesn't crash.

Are there any config/data files associated with Mindstar that I could somehow reset to their initial state?

None of our config files would have any effect on this.

You have something seriously broken on your system and will require help via our support email.