Hi guys. i am playing on a Macbook Air with Mountain Lion and I can't seem to use the space bar to fight in any of the three Alone in the Dark games. I press it and an arrow key but nothing seems to happen...Thoughts?

I'm having the same problem.

did you go into the inventory/action screen and select Fight first?

As DCT said, hold the spacebar. Then press any of the arrow keys, if it's melee.
For shooting, you need to press up, as left and right is used to aim the target.

Honestly, yep. The character does a weird pushing-out thing, or block, but there's no fighting or punching.

Weird. It sounds like the game is registering that you selected the Move/Push or Search commands instead of Fight, it happens at least for me every so often, just go into the menu again and select fight and try again just make sure your standing still and then hit the spacebar+up,left or right .