@EA_Barry
Yes, I have reinstalled the game (said that already) and performed another repair.
Not doing any overclocking.
I followed the instructions for a clean boot. Main accomplishment there was to make it impossible to launch the game, because all networking was disabled and Origin wouldn't authenticate/activate the executable without a network connection to the EA servers. Do you guys test these procedures before recommending them?
Leaving the cold boot aside, I started having an intermittent symptom where the game will start, hang on a black screen until I press ESC, then display a sort of ambience image of leaves/particles and smoke animating against a sky background. The game hangs in this condition, not responding to any keypresses or closing when I press Alt+F4. I have to open the Windows Task Manager and kill the process.
However, I *have* now managed to get sound through headphones only, by reactivating the Realtek High Definition Audio device built in to my motherboard and making it the default audio device. If I plug headphones into the rear audio jack, sound works perfectly through them. Where it doesn't work is if I am trying to get sound through the HDMI connection to my home theater receiver. I previously put 75+ hours into the game that way with no issues, so it looks like I'll have to try the headphone workaround and hope for either a game patch or a driver update to undo whatever went wrong. Wish me luck.