Help! Complete game hang

[ttjph]

Playing a scenario on Bath-Templecombe (Winter Wonderland, from the Great Scenario Challenge) and I've got a save point at Masbury Summit, ready to move off after pinning down the wagon brakes.

Unfortunately, somewhere around the bridge immediately before Masbury Station, the game hangs. GPU usage drops to zero, processor continues at 50% (one of the two cores), and that's it - I have to power off if full screen, or force the game to quit if windowed. I can hear the hard disk chuntering (though that may just be Win7), but the memory usage is static and nothing seems to be actually happening.

I've verified the game files several times (blueprint cache already clear), completed a short Cajon Pass scenario without issue, and tried again with TSX off but every time I resume I get the same problem.

This is a new computer to me but I've played a few scenarios and so far it's been faultless.

What should I try next?

Thanks!