When playing long sessions I suggest stopping periodically and defraging the HD. I was playing a long game last night and eventually things locked up and I couldn't exit the game (my computer is normally very stable) and when I rebooted I did a defrag (I did the last one several days ago) the C: (especially the C:) and G: drives (installed to G:) were
very fragmented. I started getting video issues with the small map in the lower right before this happened then the entire top half of the screen went black. I haven't tried reloading the saved game yet (autosaved just prior to the final crash) so I don't know if I can continue the game or not.
I also ran into some of the "ancient artifacts", one of the weaker computer players found one that turned all planets within a set radius that were not colonized into class 9 habitable by anyone. Fortunately they did so on the edge of the cluster of stars that was my home territory and I had 2/3 uninhabitable planets there and only 3 were inhabited by the lesser empire. I managed to grab all but 3 of the newly terraformed worlds
and they have since defected to me as have the other 3 of the lesser empire. I was already #1 in everything except population.