Iphone 4s won't show display after battery replacement?

I've recently cracked my iphone 4s screen so decided to fix it. Bought a replacement screen off ebay which i installed; the quality is not as good as the original apple one. I then decided to replace the battery as i thought it was running out quickly. I bought one off ebay, i replaced it and it won't now display anything. I can hear notifications coming through and it makes the sound when i plug it in to charge and it also vibrates when i put it on silent. When i unlock it the screen only display a faint grey background which a black rectangle going vertically.
I'm quite worried as i had only just fixed my phone. Any help will be greatly appreciated.

Seems like your new battery is working, so that can be ruled out.

It definitely seems like a display issue - are you sure it has been installed correctly. Do you still have your old cracked screen. I would put this back in and see if your phone works. If it does then you know its the new screen at fault and you will need to either send it back for a replacement, or a new one.