Currently in the middle of iPhone 5 surgery! Need a little help.

Background

I dropped my phone in water a while ago and it was water damaged. I plugged in my friends funcitoning screen into my phone and it worked. So I knew it was my screen that was water damaged.

Recently I ordered a new screen on ebay. It was not the whole front assembly (It excluded the front facing camera, home button, and heatsink/shield).

After installing my old front facing camera, home button and what not, my phone still did not turn on... (I charged it for 12 hours also)

MY QUESTION is, what could be the problem?

Possible Problems:

1. The battery is dead (wouldnt the phone still turn on if it is connected to a wall outlet?)

2. The front camera, home button etc. are damaged and somehow intefering with my phone

3. The screen I ordered from eBay is faulty.

4. ??????

Any help would be greatly appreciated. Thanks.