I wonder if it related to a second monitor issue.. a low FPS as you observed is a problem when a window spans both screens. Perhaps at some time you had a SS in a window on a second monitor, now the windowed SS wants to start there but can't... and dies. Possibly a bad location left in a registry.... Just wild guesses here

Thanks for the suggestions, but...
I've never had two monitors on this PC. The video card does have two-monitor capability, but display properties indicates that Monitor 2 is "not active" (in other words, nothing is connected to that monitor port).
The low FPS is because this is a wimpy video card (ATI X300). However, FPS in windowed mode is now better (newer driver).
Oh, and the MA3 crash comes when trying to transition from windowed to fullscreen mode (after first having transitioned from fullscreen to windowed).