iPod classic 6th generation 160GB

Charging and transferring media to/from your iPod is important.

First, try using a different 30-pin cable to make sure a faulty cable isn't the issue. Make sure you're using an official Apple 30-pin connector or an MFi-certified third-party 30-pin connector.

If you still face issues after trying other cables, your iPod's 30-pin connector may be failing. In this case, it may need to be replaced with a new connector. To my knowledge (I could be wrong here), I do not believe that Apple performs these types of repairs for these older devices, so you will likely need to look to well-reputed third-party repair shops to troubleshoot and give repair estimates for your iPod's 30-pin connector port.