today my iphone 4 home button replacement came. and before i start disassembling the phone to replace it i was wondering if i have to apply adhesive again?
or i am good to go?
If you replaced the actual home button itself, It probably wouldn't be fixed. It likely wasn't your button. The button is just s little plastic disc that covers the contact in the flex cable. Not much can really go wrong with a plastic button. The problem you are having is more likely a bad flex cable. If the flex cable is good, the metal disc that the flex cable rests on may have slipped out of place. Does your button still click? or does it press down without any tactile response?
Replacing the flex cable isn't that hard. Same process as replacing the button and as an extra step, peel the adhesive off the new cable, attach it to your home button, then thread it through the midplate to the backside. you will see the lever type connector that it connects to.
I fix iPhones & iPods at a shop 15-20 hours a week, feel free to PM if you need help.