Bottom half of screen doesn't respond correctly

A few things to consider here:

• The logical thing to suspect is the screen. If you are confident it is good (can you put it back on the original device it came from to confirm?), then move on to the next item
• There may be a partial connection only so check the digitizer connector. Also, it should have a little black foam on top of the metal plate on the flex (look at this picture). That allows it to stay firmly connected under the bracket. Don't underestimate the importance of this.
• You could have a problem on the logic board with the Touch IC. If the phone was bent in the past or dropped often over it's lifetime, this is a possibility. This would require a micro-soldering repair.