Need help with collisions

Okay, so I’m sure the answer to this is really obvious, but it’s been driving me up the wall for the longest time. I’ve got this player-character mesh, and I’m trying to make it so a cube will have it’s health bar decreased whenever it runs into the PC mesh while the left Shift button is pressed. Can anyone help me understand what I’m doing wrong?

Here’s a link to the .blend file, so you can see it for yourself: http://www.mediafire.com/?qc4teitdumniec2