Also, if you changed any of the startup settings, you can try deleting the file galciv\Data\Prefs.ini. I had a problem where the game would lock upon start if I changed anything on the race screen, and that would allow the game to start up.
I wanted to play a simple game with only one other civilization in a middling-sized galaxy, to give me a chance to get a few planets, see how things work, and all that. After exiting that game, the game hung on start-up; just sat there, accessing the hard drive, putting the CPU up to 100% utilization. debug.err gets as far as "Creating race setup screen". To get the game back again, I have to delete the file Data\prefs.ini.
That was one of the (few) cool things about Ascendancy, if I remember correctly ... some of the alien races looked *really* alien!
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