Radio Problems

A couple of months ago, you guys helped me figure out the correct wiring for an aftermarket Kenwood radio that I installed. I connected the proper wires and grounded the unit to a bolt on the steering column. I connected the harness and left the unit on my floor(I'm leaving the original in the dash). Everything worked beautifully for the first 3-5 times I drove the car. When I came back to try it again a week or so later, I connected the unit and it did not work. I checked the fuse in the radio--it is fine. With the key forward, I used a test light and confirmed that all hot wires are still hot coming from the dash. The harness has a solid connection, clicking firmly into place, and the wiring inside of it looks perfectly fine on both ends. The unit has a detachable face, but that seems to connect properly as well.

The radio has not been used heavily, and to my knowledge, it is a decent model. Is the column not a good ground? Is it possible that the radio got some type of shock from moving around a little on the carpeted floor? What are your thoughts? I don't have another radio to test, and I'd hate to replace the radio and find out that it is something else. Any replies are appreciated. Thanks a lot.