I have played this game numerous times before on the same computer with the same win 7 installation, and little changed since my last run of the v1.13 mod, but now, the game won't even start. No messages, no alerts, the process doesn't even show up in task manager. I have tried running just the vanilla game, uninstalling, reinstalling, changing location, but not even a hint of what's wrong shows up. The only possible new thing might be the installation of AVG antivirus, but it shows no problem, so... any thoughts?

Hmm, I always thought that AVG is crap (Avast FTW :D). Try dissabling it for a while and let's see what happens.

I find it very odd that you should say updating your antivirus turns off most features. This is not what antiviruses do. You really should try disabling it manually.

i have a perfect solution for your question if you game is crashing or lagging in performance or you are facing some of the problems while playing then just download the xmodgames app for smooth gameplay experience you would have no problem ahead in future if you play it with the it runs your game on it's server online