Why doesn't my speaker work when it's on and plugged in?

I just got this Harman-Kardon-CN-04N567-48220 from my grandmother's place and I decided to use it as a second set of speakers for 4-way surround sound with a subwoofer.

The problem I am having is that after wiring everything in correctly and powering it on, it doesn't seem to work in either speaker unless I push on the wire really close to the speaker that has the power directly channeled to it.