There are two problems with these button types; The first is that they seem to attract moisture which can break the connection, this is why the home button on the iPhone 4 can slowly get less responsive over time. Check out this guide to help you diagnose any moisture damage inside the device. Also, to access the home button, check out this home button installation guide. The second is that Apple chose to give the foil part of the button a little nipple like bit which raises it by less than a mm and this sometimes goes wondering around and this makes the external button sit that bit lower and not fully work. The fix for this is to put a tiny 1x1mm bit of 3M tape on the centre of the button and it should work. If this option doesn't release the button then the disk has probably gone flat and you will need a new home button.