Show the charghing icon but wont charge

Hey, i have an iphone 4 that came to my lab with a problem, the iphone show the chatghin icon but wont charge at all(i checked on the computer i checked wite a regular charger, i cheked with a diffrent cable and charger but it wont charge)

I restore to ios 7, i changed the battery tuice, i changed the dock connector, and still after all that steps it wont charge!

What could it be?