Weird X-axis behavior - Folger Tech Prusa i3 Aluminum. Help!

I've been messing with this thing for quite a while, and I don't seem to be getting anywhere. I assembled it exactly as they have it described in the build guide, but I'm thinking something isn't right with the firmware settings out of the box.

From a fresh start without homing the X and with the X carriage centered, it will allow it to move right (negative) but not left (positive), so it only travels one way. If I then home it, it will move slightly to the right and read a coordinate of 0, but not travel to the end stop. It keeps moving a bit every time I hit home.
From there it gets even more interesting. When I try to move it positive, it doesn't respond but the number in Repetier will increase. So if I move it +5, it will read 5. Then when I tell it to move in negative steps, it actually WILL move, but only til it reaches coordinate 0 and hits an invisible wall.


Holding the end stop has some a similar effect. I've tried changing the logic in the firmware several times, and nothing seems to fix it. Any help would be appreciated!

Here is the guide I followed.

Here is the default Configuration.h settings.