[HELP]Collision detection not working

Hi guys, I am totally new to Unity as well as game developing.

For now, I am trying to follow the Roll-a-Ball project

I do everything as the Video told me to do, but everytime I press the Game, the ball (player, and the wall around just keep falling through the plane and to nowhere to be seen). I have seen everybox, and try check/unchecking everything but still, if I set use gravity on, the ball still fall, right through the ground, like there is no collision detected between them.

As if I turn of the gravity, I can actually move the ball around fine, but still, the ball would run through the wall,like there is no collision between them, so I don't really know what to do.

I am running on Windows 8 32 bits, with the latest version of Unity, I had tried re-install Unity but it didn't work.

Thanks for reading

 

Did you attach colliders to the objects?