I bought a game i cant even play on single player or multiplayer it kinda sucks.
If you can't play single player then something is wrong with your computer.
As suggested, uninstall the game.
Make sure you have the latest video and sound card drivers.
Reinstall game.
Launch Impulse and make sure you have the latest Demigod patch.
Play and have fun!
If it's still not working after then then contact support directly with your exact error messages and such. But make sure you do the above first.