Why isn't my screen working?

Hello, I was recently given an iPhone 5 by my girlfriend since my old phone had died, I believe she had it for 3 years and tha battery was very worn out but it did work. Eventually the battery completely died so I opted to replace the battery myself since I have done that with phones in the past. Long story short I replaced the battery but the screen wouldn't turn on at all, so I replaced the screen with one I bought from iFixer and it turned on after some charge.

The problem now is I can only access the phone itself when it is on charge, if I take it off the phone stays on but it only shows a black screen but the backlight is on, when I plug it into the charger it comes up as it should with home screen. It will only turn on if I do a hard reset on charge.

Anyone know why it would show a black screen?