Hello, Is your iPhone working besides the black screen? Maybe if you restore it with iTunes it might come back on, but if iTunes recognizes the iPhone then my guess is a dead screen
If you have a hot air station you can try reflowing it, his worked for me. Just heat up the baseband chip and maybe it will work after that. Let me know!
Hello, In what country do you live? I can do it for you for a good price if you'd like. Or if you want to do it for yourself : you NEED a hot air station to replace the WiFi IC, replacing the antenna only wouldn't change anything.
You can at first try another battery, if that doesn't work check the battery connector (especially the middle 2 pins). When it is at the charger, does it drop percentage or does it just not change? You can also try charging it when powered off for 1 hour and then check again.
You have to place it between the logic board and battery (the top screw) It does not really do anything for your phone,it just puts pressure on the antenna.