It could be SO many things! Could be the replacement screen was DOA, or perhaps it was damaged during your install. It could also be something else was the original culprit. My guess would be that you damaged something during the install of the screen, it's VERY easy to do unfortunately.
a new flex cable sorted the problem screen and touch screen work fine. only problem is it wont make or recieve calls. think this may be because i brought it off ebay prehaps stolen/lost handset???