Try these steps one at a time:
1) Update your video drivers with a clean install.
a) Download the new drivers from your video card manufacturer's website. Usually www.nvidia.com, www.ati.com or www.intel.com.
Un-install the old drivers and reboot
c) Cancel the Found New Hardware wizard when you log back into Windows
d) Install the new drivers that you downloaded
If you have the most updated drivers but you did not do a clean install when you updated, you may want to re-install your drivers using the method above.
2) Update your sound drivers.
3) Update to the latest version of Gal Civ 2.
4) Install Smart Exception from the Free Stuff tab in Stardock Central. This generates a crash report when GC2 crashes (unless the computer has locked up or reboots itself) which is useful to us in determining where the crash is occurring. We will also want your debug.err file. If you are constantly getting crashes and you need help from a support tech, e-mail support@stardock.com. Otherwise, e-mail the crash log and the debug.err file to gc2bugs@stardock.com. If you have a save game that consistently crashes within a set amount of turns, send that in as well, but you will probably need to zip it.
5) Go to the advanced tab of your display properties and find the Direct3D settings.
a) Set Antialiasing to be Application Controlled
Set AnsioTropic filtering to be Appliation Controlled
c) Set Image Settings to be Quality
6) Make sure that your desktop resolution is at least 1024 x 768 at 32 bit color. You may want to try higher resolutions if your video card and monitor support them, but you always want to be at 32 bit color, and the game resolution should never be higher than the desktop resolution.
7) In your My Documents\My Games\GalCiv2 folder, there is a prefs.ini file. You can change the video settings there.
a) Set Multisample = 0 to disable anti-aliasing, particularly if you have an error in your debug.err file about failing to create a device.
Set HardwareMouseCursor = 1
c) Set Fullscreen = 0 to run in a window. If the game resolution is the same size as the desktop resolution, it will still appear to be fullscreen.
d) If your crashing is occurring after the intro, try setting SkipIntro=1
8) Check to see what codecs you have installed. Many media player programs like WinDVD or Media Portal install codecs on your system and they don't always play nice with other programs. To see what codecs are installed on your system:
9) Turn off all the music and sfx in the game. You may also want to try disabling your sound card. If this works, there may be some issue with your sound driver that un-installing the codecs didn't fix. You may need to re-install your sound drivers after having un-installed your codecs, or you may be able to fix the problem by changing your audio acceleration.
a) Right click on the My Computer icon and select properties.
Click on the hardware tab
c) Click on the Device Manager button.
d) Right click on Audio Codecs and choose properties. The properties tab of the dialog that comes up will list and allow you to remove the audio codecs installed on your computer. e) You can follow the same steps for the Video Codecs.
f) There are instructions in this MSDN article for re-installing the Windows audio and video codecs:
http://support.microsoft.com/?scid=kb;en-us;893681&spid=1007&sid=1498#EUADAAA
10) Run dxdiag and the Direct3D and DirectSound tests to make sure that there is nothing wrong that DirectX can detect
a) Click on your windows start button
Click on Run
c) type the word dxdiag in the dialog box and click OK.
d) Allow it to check to see if your drivers are digitally signed, let it run its tests
e) Run the Direct3D and DirectSound tests.
f) Click Save all information and save the file somewhere you'll be able to find it.