iPod touch no longer wokring 2 weeks after screen replacement

I've recently repaired an iPod Touch with a broken display and everything went well. I had no special issues during the repair or after. I tested all functionnalities before delivering the apparel back to the customer, cameras, wifi, touch, charging, computer sync.. etc.

Unfortunately she came back yesterday and told me that nothing was working anymore. I tried testing the device but it's a 100% unresponsive. No charging, no itunes detection, nothing at all.

Before I start to tear this thing appart, I actually wonder where to look. Could the iPod had any other damages caused? And also what should I do with this situation, I'm quite lost on solution at this point.

Thanks in advance!