EDIT: This is solved. It turns out enabling the Discord Overlay for PA:T breaks the game. I turned it off and the game works fine now. Starting yesterday, every time I launch PA:T from my Steam library, the game gives me a black screen. Attempting to alt-tab doesn't work, and clicking or pressing keys prompts Windows to tell me that the app is not responding. Closing it from here (using Windows to kill the process) works fine, but nothing else (alt-tabbing, etc.) does. This (obviously) concerns me, and if anyone knows what's wrong and/or how to fix it, some assistance would be much appreciated.
Thank you. At first, I thought this list would be useless, but while looking through it, I was reminded of the Discord Overlay, which I had recently enabled for PA:T. Turns out the overlay breaks the game. So, again, thanks for pointing me to the solution.