Replaced Interconnect Cable On iPhone 5 Now Won't Turn On

My friend gave me two iPhone's (5) so I can replace the housing of one working iphone with the other one that's broken. I did it and gave him the working one. Then he tells me to fix the one that won't turn on, so another friend lent me his iphone so i could use his battery on the broken one to see if its the battery thats faulty and to my surprise it was. So I ordered a battery online and installed it but during the installation I broke one interconnect cable and took it out and closed it. I turned it on and it worked so i turned it off and ordered the cable. When the cable arrived, I opened the iphone connected it and closed it. Now it won't turn on and does nothing. I have tried everything, I did a hard reset, I plugged it into the wall and computer, I opened it and took it apart, put it back together again perfectly and it still does not turn on. I have one week before I need to give it back. HELP!