fixing collisions

Okay, so I know that this is a lame question with a (probably) really simple answer, but I can’t figure it out to save my life: I’m trying to get a player-character mesh to affect a cube’s health bar when the left-shift button is pressed while close to it. However, no matter what I do, the meshes simply will not collide with each other for any reason. Plus, the mesh looks hideous, but I can look up stuff on Youtube to solve that problem easily. So, I’ll put the .blend file here, and see if there’s anything I can do to make this work.

Here’s the link: http://www.mediafire.com/?dya9efa5vg53577