Samsung S3 SGH-I747 won't power up after USB replacement

[The Robman]

I replaced the USB port on my wife's S3 and it worked perfectly, then I replaced the USB on my son's S3 but once it was done, the phone would not power up at all, and nothing happens when I connect it to the PC. I took it to a phone shop and they re-replaced the USB but the phone still won't power up. Any ideas?

 

[The Robman]

Ok, so maybe this isn't the right forum for a hardware question, could anybody recommend a better place to ask this?