Default Galaxy S3 wont turn on or charge but connects to the computer

Hello, I have an sgh-i747 it was running task650s rom and one day it just randomly shut off. I tried everything and was told to buy a jig to put the phone into download mode. I bought a jig, plugged it in, still nothing. When I plug it into the computer it shows up as QHSUSB_DLOAD #3 (im using a mac).

What should I do next? All I did was plug the jig into the USB but nothing happened.

This is the jig I bought
http://www.ebay.ca/itm/271353549321?...84.m1497.l2649