My 3 year old AT&T iPhone 4 had a temperamental Home Button and a battery that had lost a lot of its capacity. I decided to replace the two components to extend the life of the iphone until the next generation is released (iPhone 5s? iPhone 6?)
The repair was how-to story of what NOT to do. I took great care during assembly, but I wasn't careful enough. I didn't realize that while trying to separate the screen from the frame, I was pulling against the two ribbon cables. I ended up damaging the longer of the two cables which is responsible for the digitizer function. The damage either occurred during the separation or the re-assembly. Be absolutely sure that the longer cable is fed through all the way and not folded upon itself. Upon re-assembly I had a perfectly functioning Home Button and a new battery but a phone that had no digitizing function...esse
When reinstalling the screen, triple check to make sure that the longer, thinner screen ribbon cable is pulled through fully and not folded onto itself.