Troubleshooting:

If you get an access violation on start up:

A - Make sure the normal game works so that you know it’s not something like a video driver or a bad installation causing the problem.

B - Make sure you’re not doing anything crazy like running the game from a cloud drive or over a usb cable. (and that you actually bought the game. haha)

C – turn the video settings all the way down

D – Uninstall Homeworld, delete the folder '\steamapps\common\Homeworld\HomeworldRM\DataWorkshopMODs’, then reinstall the game
If that doesn’t do it, then I don’t think I can help you any further. Buy a new computer? =D

If you get an access violation during the game or if the textures and buttons look like a bunch of red checkers, turn the video setting 'texture size limit' ALL THE WAY down. Then if it works you can try incrementally turning it back up. Playing with fewer race types in the game should work too. (Make sure at least one is Hiigaran or the AI might not work)

If the AI sucks or it doesn't build anything:

A - make sure at least one player is set to Hiigaran (this is fixed - doesn't matter)

B - Like before, turn the video setting 'texture size limit' ALL THE WAY down. Then if it works you can try incrementally turning it back up. Apparently the 'thinking' of the game uses the same memory as drawing stuff. For Multiplayer the host should probably turn this down as well.