How to troubleshoot my Home button

Is the black button which is present at the screen in the proper location and free to move up and down, to push button? Is the Front Screen Assembly perfectly down and back into place?

If still problem, carefully open iPhone, and look at underside base of Front Assembly, are the two small gold/copper contacts of the Home Button Ribbon Flex present and in perfect shape, ie not missing or flattened? With a volt meter you can check for completion of Home Button Flex circuit, when you press the Home Button the curcuit is complete. Check to make sure that the Dock Flex Cable #4 is seated perfectly to the Logic Board. The Home Button information reaches the Logic Board through Flex #4. Also, I doubt this is the problem, but under the Home Button Pad (which is under the Home Button) there is a small silver metal disc glued to the Mid Frame, it must be there and centered for smooth Home Button function.

Maybe Flex #4 just needs to be reseated correctly.