I have the same problem with Beyond the Sword and it doesn't give any error message, it just won't run anymore. I'm using Vista 64-bit, intel E8500 3,16Ghz, Ati Radeon 4850 and 4Gb Ram. The game was working perfectly just few days ago, Civ4 and Warlords are running still ok.
In task manager there is a process: Civ4BeyondSword.exe *32, usage about 50%. However there is nothing in application page. And nothing happens.
I updated my drivers, directx and os, tried to run vista in safe mode but nothing seems to help.
edit: I have the complete edition of the game (in case it matters somehow)