First, you'll need to make sure the cable is the problem. To do this, take the cable out, and test it in a USB port you know works (such as in your computer). If the cable can still charge a phone, then the port is the problem.
We've put together a handy video on how to check and change a Kippax's cables.
If the cable is the issue, you can simply order another from Chargebar's website, or for more value, pick up a cable pack.