The most common issue with iPad Mini is that when you close the new screen the LCD cable attaches to the adhesive on the frame and is folded and broken. This is super delicate and I screwed up some screens before I understood this. Take a look at the image. When you remove the bottom adhesive make sure the cable does not stick to the adhesive on the glass. When you close the screen start from the top. Then use a spudger and tuck the cable so it goes inside the frame before you close it. I had some good pictures of this on the guide but they seem to be gone for some reason.
I am afraid if this is the issue you will have to buy a new screen as the cable is useless once you have folded it.
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