If reinstalling did not work, and you did not have old custom races, could you please try the following:
a) Could you please send me the 'Player' and 'Player-prev' log files to email@example.com (or attach them here in a post)? The log files can be found in this folder: C:\Users\<your_username>\AppData\LocalLow\Praxis Games\ISG\
b) When you start your game, are you using 'New Game', 'Load Game' or 'Continue' in the main menu? If you are using 'Continue' or 'Load Game', that may be the issue because old save files are not compatible with version 1.3.4 anymore.
c) Steam files may have become corrupted. Occasionally, Steam files can become corrupted which makes the game unable to run. To fix this, please verify your files/cache integrity. Here's a procedure on how you can do that: https://support.steampowered.com/kb_article.php?ref=2037-QEUH-3335
d) Your Antivirus or firewall software may be blocking the game. Try adding the game as an exception in your firewall / antivirus, if you have any.
e) Have you tried reinstalling in both Steam and GOG and see if that helped?
Let me know if anything of the above helped. And please send me the log files as that will be very helpful in determining the cause of the issue.