iTunes won't recognize iPod

Here's the situation. When I connect my iPod classic via USB cable, it does not show up in either Finder or iTunes; it does not even appear to be charging, so I assume the Macbook is not recognizing it at all. Similarly, when I connect it to the iPod dock on my stereo system, the display reads "no connection". I began to wonder if there was an internal problem with the iPod, but then I connected it to a wall charger, and it began charging like normal. I updated to the most recent version of iTunes and tried using a brand new USB cable, but to no avail.

Has anyone experienced this problem and/or discovered a solution? Thanks in advance.

P.S. One piece of information that might be useful. I visited the Apple Store last week and had my hard drive replaced. However, the iPod was syncing like normal for the first five days afterward, and then the Macbook abruptly stopped recognizing the iPod.